Metallic Nanofiber Ink, Substantially Transparent Conductor, and Fabrication Method

ABSTRACT

An exemplary printable composition comprises a liquid or gel suspension of a plurality of metallic nanofibers or nanowires; a first solvent; and a viscosity modifier, resin, or binder. In various embodiments, the metallic nanofibers are between about 10 microns to about 100 microns in length, are between about 10 nm to about 120 nm in diameter, and are typically functionalized with a coating or partial coating of polyvinyl pyrrolidone or a similar compound. An exemplary metallic nanofiber ink which can be printed to produce a substantially transparent conductor comprises a plurality of metallic nanofibers; one or more solvents such as 1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone, cyclohexanone, cyclopentanone, 1-hexanol, acetic acid, cyclohexanol, or mixtures thereof; and a viscosity modifier, resin, or binder such as polyvinyl pyrrolidone or a polyimide, for example.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application as a continuation of and claims priority to U.S. patentapplication Ser. No. 13/360,999 filed on Jan. 30, 2012, which is anonprovisional and conversion of and, under 35 U.S.C. Section 119,claims the benefit of and priority to U.S. Provisional PatentApplication Ser. No. 61/447,160, filed Feb. 28, 2011, inventors Mark D.Lowenthal et al., both titled “Metallic Nanofiber Ink, SubstantiallyTransparent Conductor, and Fabrication Method”, and the related U.S.patent application Ser. No. 13/598,418, filed on Aug. 29, 2012 andissued Jun. 4, 2013 as U.S. Pat. No. 8,454,859 is also a continuation ofand claims priority to U.S. patent application Ser. No. 13/360,999, allof which are commonly assigned herewith, the entire contents of whichare incorporated herein by reference with the same full force and effectas if set forth in their entireties herein, and with priority claimedfor all commonly disclosed subject matter.

FIELD OF THE INVENTION

The present invention in general is related to conductive inks andpolymers utilized to produce a substantially transparent conductor and,in particular, is related to a composition of metallic nanofiberssuspended in a liquid or gel and capable of being printed, substantiallytransparent conductive films and manufactures having the metallicnanofibers, and methods of manufacturing a composition of metallicnanofibers suspended in a liquid or gel to form a metallic nanofiberink.

BACKGROUND OF THE INVENTION

Many conductive inks include a particulate metal, such as silver oraluminum, in a binder or binding medium. While such inks produceconductors (when cured) which are substantially conductive and have acomparatively low electrical impedance (or resistance), the resultingconductors are substantially opaque and do not allow the transmission ofany appreciable amount of light in the visual spectrum or otherimportant spectra, such as ultraviolet and infrared spectra.

Optically transparent conductors are needed in a wide variety ofapplications, however. For example, optically transparent conductors arehighly desirable for making electrical contacts to diodes inphotovoltaic and in light emitting applications, to allow greater lightinput and light output, respectively, compared to opaque conductors.

Typical printable transparent conductors, while having reasonableoptical transmissivity, unfortunately often have a comparatively highelectrical impedance and low conductivity when cured, with resistancestypically in the range of 800-1000 or more ohms per square (e.g.,polyethylene-dioxithiophene). In addition, many such transparentconductors (e.g., indium tin oxide (ITO)) require specialized depositiontechniques and very high temperature processing to reduce impedance, orwhen cured in a resulting apparatus, tend to have limited, if any,flexibility. The inks or polymers to produce such typical transparentconductors include, for example, polyethylene-dioxithiophene (e.g.,“Orgacon” from AGFA Corp. of Ridgefield Park, N.J., USA), a combinationof poly-3,4-ethylenedioxythiophene and polystyrenesulfonic acid(marketed as Baytron P and available from Bayer AG of Leverkusen,Germany), a polyaniline or polypyrrole polymer, carbon nanotubes (CNTs),and/or antimony tin oxide (ATO) (with the CNTs, ATO or others typicallysuspended as particles in any of the various binders, polymers orcarriers).

Other printable transparent conductors require significant additionalprocessing after printing. For example, some are created as separateunitary sheets or films which must be laminated onto a substrate, andthen subsequently patterned to form the desired, electrically isolatedconductors having specific electrical connections, such as through anetching process. Other printable transparent conductors also requiresignificant additional processing following deposition, such as acidwashing followed by significant physical compression in nip rollers, forexample, in order to create conductive connections among metallicnanowires forming the conductors. Other printable transparent conductorsare fragile when deposited, and may further require additionalstabilization layers to hold the deposited but unstable metallicnanowires in place. These types of printable transparent conductors havelimited usefulness, however, as they cannot be readily utilized toprovide electrical connections to devices, such as diodes, which arealready placed on a substrate and which should not be subjected topotentially irreparably damaging treatments such as acid washes,etching, or compressive forces, for example.

Accordingly, a need remains for a conductive ink, polymer or compositionwhich may be printed and, when cured, produces a resulting conductorwhich is stable, fixed in place, and capable of providing electricalconnections to devices, and further provides a comparatively lowelectrical impedance (or resistance) while simultaneously allowingsubstantial light transmission in the visual or other spectra. Inaddition, a need remains for such a composition to be capable of curinginto a stable conductor at comparatively lower processing temperatures,and be suitable for a wide variety of applications, such as for use inlighting and photovoltaic panels.

SUMMARY

The exemplary embodiments provide a “metallic nanofiber ink”, namely, aliquid or gel suspension of metallic nanofibers which is capable ofbeing printed, such as through screen printing or flexographic printing,for example and without limitation, to produce a substantiallytransparent and stable conductor when cured or solidified. An exemplarymethod also comprises a method of manufacturing metallic nanofiber inkwhich, as discussed in greater detail below, suspends a plurality ofmetallic nanofibers in a solvent and viscous resin or polymer mixturewhich is capable of being printed to manufacture various devices, suchas light emitting diode (LED) devices and photovoltaic devices.Exemplary apparatuses and systems formed by printing such a metallicnanofiber ink are also disclosed.

An exemplary composition comprises a plurality of metallic nanofibers,substantially all of the metallic nanofibers at least partially coatedor functionalized with a polymer; a first solvent; and a viscositymodifier, resin, or binder. In various exemplary embodiments, themetallic nanofibers have lengths between about 1μ and about 250μ anddiameters between about 10 nm and about 500 nm; or more particularly,the metallic nanofibers have lengths between about 10μ and about 150μand diameters between about 5 nm and about 250 nm; or more particularly,the metallic nanofibers have lengths between about 10μ and about 100μand diameters between about 10 nm and about 100 nm; or moreparticularly, the metallic nanofibers have lengths between about 10μ andabout 80μ and diameters between about 10 nm and about 80 nm; or moreparticularly, the metallic nanofibers have lengths between about 1μ andabout 60μ and diameters between about 10 nm and about 200 nm; or moreparticularly, the metallic nanofibers have lengths between about 10μ andabout 70μ and diameters between about 25 nm and about 60 nm. Lastly, invarious other exemplary embodiments, the metallic nanofibers havelengths between about 40μ and about 60μ and diameters between about 15nm and about 40 nm, and/or have lengths between about 10μ and about 25μand diameters between about 10 nm and about 15 nm.

In another exemplary embodiment, the plurality of metallic nanofibershave an aspect ratio between about 500:1 to 100:1. In another exemplaryembodiment, the metallic nanofibers have an aspect ratio between about400:1 to 200:1. In another exemplary embodiment, the metallic nanofibershave an aspect ratio between about 350:1 to 250:1. In another exemplaryembodiment, the metallic nanofibers have an aspect ratio between about350:1 to 275:1.

In an exemplary embodiment, the plurality of metallic nanofiberscomprises at least one metal selected from the group consisting of:aluminum, copper, silver, gold, nickel, palladium, tin, platinum, lead,zinc, alloys thereof, and mixtures thereof.

In an exemplary embodiment, the metallic nanofibers are functionalizedwith a coating or partial coating of a polymer. In another exemplaryembodiment, the metallic nanofibers are functionalized with a coating orpartial coating of a pyrrolidone polymer. In another exemplaryembodiment, the metallic nanofibers are functionalized with a coating orpartial coating of polyvinyl pyrrolidone (PVP), generally in an amountof between about 0.09% to about 0.20% by weight of the coated metallicnanofibers. In various other exemplary embodiments, the metallicnanofibers are functionalized with a substantial or complete coating ofpolyvinyl pyrrolidone (PVP) having a comparatively low molecular weight.In another exemplary embodiment, the metallic nanofibers arefunctionalized with a substantial or complete coating of polyvinylpyrrolidone having a molecular weight between about 5,000 to about50,000 MW. Other types of coatings or functionalizations, including withdifferent polymers, mixtures of polymers or other materials, are alsowithin the scope of the disclosure.

In an exemplary embodiment, the first solvent comprises at least onesolvent selected from the group consisting of: water; alcohols such asmethanol, ethanol, N-propanol (including 1-propanol, 2-propanol(isopropanol or IPA), 1-methoxy-2-propanol), butanol (including1-butanol, 2-butanol (isobutanol)), pentanol (including 1-pentanol,2-pentanol, 3-pentanol), hexanol (including 1-hexanol, 2-hexanol,3-hexanol), octanol, N-octanol (including 1-octanol, 2-octanol,3-octanol), tetrahydrofurfuryl alcohol (THFA), cyclohexanol,cyclopentanol, terpineol; lactones such as butyl lactone; ethers such asmethyl ethyl ether, diethyl ether, ethyl propyl ether, and polyethers;ketones, including diketones and cyclic ketones, such as cyclohexanone,cyclopentanone, cycloheptanone, cyclooctanone, acetone, benzophenone,acetylacetone, acetophenone, cyclopropanone, isophorone, methyl ethylketone; esters such ethyl acetate, dimethyl adipate, proplyene glycolmonomethyl ether acetate, dimethyl glutarate, dimethyl succinate,glycerin acetate, carboxylates; glycols such as ethylene glycols,diethylene glycols, polyethylene glycols, propylene glycols, dipropyleneglycols, glycol ethers, glycol ether acetates; carbonates such aspropylene carbonate; glycerols such as glycerin; n-methylpyrrolidone,acetonitrile, tetrahydrofuran (THF), dimethyl formamide (DMF), N-methylformamide (NMF), dimethyl sulfoxide (DMSO); acids, including organicacids such as carboxylic acids, dicarboxylic acids, tricarboxylic acids,alkyl carboxylic acids, acetic acid, oxalic acid, mellitic acid, formicacid, chloroacetic acid, benzoic acid, trifluoroacetic acid, propanoicacid, butanoic acid; bases such as ammonium hydroxide, sodium hydroxide,potassium hydroxide; and mixtures thereof.

In an exemplary embodiment, the viscosity modifier, resin or bindercomprises polyvinyl pyrrolidone (also known or referred to as polyvinylpyrrolidinone), polyvinyl alcohol, or mixtures thereof. In anotherexemplary embodiment, the viscosity modifier, resin or binder comprisesor further comprises a methylcellulose resin, such as a hydroxy propylmethylcellulose resin, or a hydroxy methylcellulose resin, or mixturesthereof. In another exemplary embodiment, the viscosity modifier, resinor binder comprises a polyimide.

In an exemplary embodiment, the viscosity modifier, resin or bindercomprises at least one viscosity modifier, resin or binder selected fromthe group consisting of: polymers (or equivalently, polymeric precursorsor polymerizable precurors) such as polyvinyl pyrrolidone (also referredto or known as polyvinyl pyrrolidinone), polyvinyl alcohol, polyimidepolymers and copolymers (including aliphatic, aromatic and semi-aromaticpolyimides), acrylate and (meth)acrylate polymers and copolymers;glycols such as ethylene glycols, diethylene glycol, polyethyleneglycols, propylene glycols, dipropylene glycols, glycol ethers, glycolether acetates; clays such as hectorite clays, garamite clays,organo-modified clays; saccharides and polysaccharides such as guar gum,xanthan gum; celluloses and modified celluloses such as hydroxymethylcellulose, methylcellulose, ethyl cellulose, propylmethylcellulose, methoxy cellulose, methoxy methylcellulose, methoxypropyl methylcellulose, hydroxy propyl methylcellulose, carboxymethylcellulose, hydroxy ethylcellulose, ethyl hydroxyl ethylcellulose,cellulose ether, cellulose ethyl ether, chitosan; fumed silica, silicapowders, modified ureas; and mixtures thereof.

In various exemplary embodiments, the composition further comprises asecond solvent different from the first solvent. In an exemplaryembodiment, the second solvent is at least one solvent selected from thegroup consisting of: water; alcohols such as methanol, ethanol,N-propanol (including 1-propanol, 2-propanol (isopropanol or IPA),1-methoxy-2-propanol), butanol (including 1-butanol, 2-butanol(isobutanol)), pentanol (including 1-pentanol, 2-pentanol, 3-pentanol),hexanol (including 1-hexanol, 2-hexanol, 3-hexanol), octanol, N-octanol(including 1-octanol, 2-octanol, 3-octanol), tetrahydrofurfuryl alcohol(THFA), cyclohexanol, cyclopentanol, terpineol; lactones such as butyllactone; ethers such as methyl ethyl ether, diethyl ether, ethyl propylether, and polyethers; ketones, including diketones and cyclic ketones,such as cyclohexanone, cyclopentanone, cycloheptanone, cyclooctanone,acetone, benzophenone, acetylacetone, acetophenone, cyclopropanone,isophorone, methyl ethyl ketone; esters such ethyl acetate, dimethyladipate, proplyene glycol monomethyl ether acetate, dimethyl glutarate,dimethyl succinate, glycerin acetate, carboxylates; glycols such asethylene glycols, diethylene glycols, polyethylene glycols, propyleneglycols, dipropylene glycols, glycol ethers, glycol ether acetates;carbonates such as propylene carbonate; glycerols such as glycerin;n-methylpyrrolidone, acetonitrile, tetrahydrofuran (THF), dimethylformamide (DMF), N-methyl formamide (NMF), dimethyl sulfoxide (DMSO);acids, including organic acids such as carboxylic acids, dicarboxylicacids, tricarboxylic acids, alkyl carboxylic acids, acetic acid, oxalicacid, mellitic acid, formic acid, chloroacetic acid, benzoic acid,trifluoroacetic acid, propanoic acid, butanoic acid; bases such asammonium hydroxide, sodium hydroxide, potassium hydroxide; and mixturesthereof. Additional different third, fourth, or more solvents may alsobe utilized.

In an exemplary embodiment, the metallic nanofibers are present in anamount between about 0.01% to 3.0% by weight. In various other exemplaryembodiments, the metallic nanofibers are present in an amount betweenabout 0.03% to 2.5% by weight; or more particularly, an amount betweenabout 0.05% to 2.0% by weight; or more particularly, an amount betweenabout 0.05% to 1.5% by weight; an amount between about 0.075% to 1.0% byweight; or more particularly, an amount between about 0.14% to 0.75% byweight; or more particularly, an amount between about 0.15% to 0.55% byweight; or more particularly, an amount between about 0.16% to 0.35% byweight; or more particularly, an amount between about 0.17% to 0.32% byweight; or more particularly, an amount between about 0.18% to 0.30% byweight; or more particularly, an amount between about 0.20% to 0.29% byweight; or more particularly, an amount between about 0.21% to 0.25% byweight. Lastly, in another exemplary embodiment, the metallic nanofibersare present in an amount between about 0.22% to 0.24% by weight.

In an exemplary embodiment, the first solvent comprises 1-butanol and ispresent in an amount of about 3 percent to 10 percent by weight, and theviscosity modifier, resin or binder comprises a polyimide and is presentin an amount of about 0.75% to 5% by weight.

In another exemplary embodiment, the first solvent comprisescyclohexanone, is present in an amount of about 0.05 percent to 99.95percent by weight, and the viscosity modifier, resin or binder comprisesa polyimide and is present in an amount of about 0.75% to 5% by weight.

In another exemplary embodiment, the viscosity modifier, resin or bindercomprises polyvinyl pyrrolidone and is present in an amount of about0.75% to 5% by weight, the first solvent comprises 1-butanol and thesecond solvent comprises cyclohexanol, and the first solvent is presentin an amount of about 3 percent to 10 percent by weight and the secondsolvent is present in an amount of about 50 percent to 95 percent byweight.

Another exemplary composition further comprises an organic acid presentin an amount of about 0.1% to 2% by weight, the organic acid comprisingat least one acid selected from the group consisting of: carboxylicacids, dicarboxylic acids, tricarboxylic acids, alkyl carboxylic acids,acetic acid, oxalic acid, mellitic acid, formic acid, chloroacetic acid,benzoic acid, trifluoroacetic acid, propanoic acid, butanoic acid; andmixtures thereof.

Another exemplary composition further comprises a third solvent, thethird solvent different from the first solvent and the second solvent,the third solvent present in an amount of about 0.1% to 10% by weight.In an exemplary embodiment, the third solvent is at least one solventselected from the group consisting of: acids, including organic acidssuch as carboxylic acids, dicarboxylic acids, tricarboxylic acids, alkylcarboxylic acids, acetic acid, oxalic acid, mellitic acid, formic acid,chloroacetic acid, benzoic acid, trifluoroacetic acid, propanoic acid,butanoic acid; bases such as ammonium hydroxide, sodium hydroxide,potassium hydroxide; and mixtures thereof.

In an exemplary embodiment, the first solvent is present in an amount ofabout 1% to 10% by weight and comprises at least one solvent selectedfrom the group consisting of: 1-butanol, ethanol, 1-pentanol, 1-hexanol,acetic acid, cyclohexanone, cyclopentanone, and mixtures thereof; theviscosity modifier, resin, or binder is present in an amount of about0.75% to 5.0% by weight and comprises at least one viscosity modifier,resin, or binder selected from the group consisting of: polyvinylpyrrolidone, a mixture of polyvinyl pyrrolidone with polyvinyl alcohol,and/or a polyimide; and the second solvent is present in an amount ofabout 1.75% to 98.25% by weight and comprises at least one solventselected from the group consisting of: cyclohexanol, cyclohexanone,cyclopentanol, butyl lactone, and mixtures thereof. Additional third,fourth or more solvents may also be utilized. A method of making thecomposition is also disclosed, with the method comprising, for apolyvinyl pyrrolidone embodiment: mixing the plurality of metallicnanofibers with 1-butanol and cyclohexanol, for example; mixingpolyvinyl pyrrolidone and cyclohexanol; heating the mixture of polyvinylpyrrolidone and cyclohexanol to between about 80° C. to about 90° C.;cooling the mixture of polyvinyl pyrrolidone and cyclohexanol to about25° C.; adding the mixture of the plurality of metallic nanofibers with1-butanol and cyclohexanol to the mixture of polyvinyl pyrrolidone andcyclohexanol; and mixing the plurality of metallic nanofibers,1-butanol, polyvinyl pyrrolidone and cyclohexanol for about 3 to 10minutes in an air atmosphere at standard temperature (about 25° C.) andpressure (about one atmosphere). In an exemplary embodiment, about 0.1%to 2% of acetic acid is also added.

In yet another exemplary embodiment, the plurality of metallicnanofibers are coated with polyvinyl pyrrolidone and the plurality ofmetallic nanofibers are present in an amount of about 0.01% to 3.0% byweight; the first solvent is present in an amount of about 1% to 10% byweight and comprises at least one solvent selected from the groupconsisting of: 1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone,cyclohexanone, 1-hexanol, acetic acid, and mixtures thereof; theviscosity modifier, resin, or binder is present in an amount of about0.75% to 5.0% by weight and comprises at least one viscosity modifier,resin, or binder selected from the group consisting of: polyvinylpyrrolidone, a polyimide, and mixtures thereof; and further comprising asecond solvent present in an amount of about 2.75% to 97.25% by weight,wherein the second solvent comprises at least one solvent selected fromthe group consisting of: cyclohexanol, cyclohexanone, cyclopentanol,butyl lactone, and mixtures thereof.

In another exemplary embodiment, the plurality of metallic nanofibersare coated with polyvinyl pyrrolidone and the plurality of metallicnanofibers are present in an amount of about 0.01% to 3.0% by weight;the first solvent is present in an amount of about 2.5% to 8.0% byweight and comprises at least one solvent selected from the groupconsisting of: 1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone,cyclohexanone, 1-hexanol, acetic acid, and mixtures thereof; theviscosity modifier, resin, or binder is present in an amount of about1.0% to 4.5% by weight and comprises at least one viscosity modifier,resin, or binder selected from the group consisting of: polyvinylpyrrolidone, a polyimide, and mixtures thereof; and further comprising asecond solvent present in an amount of about 4.5% to 95.5% by weight,wherein the second solvent comprises at least one solvent selected fromthe group consisting of: cyclohexanol, cyclohexanone, cyclopentanol,butyl lactone, and mixtures thereof.

In another exemplary composition, the plurality of metallic nanofibersare coated with polyvinyl pyrrolidone and the plurality of metallicnanofibers are present in an amount of about 0.01% to 3.0% by weight;the first solvent is present in an amount of about 2.5% to 8.0% byweight and comprises at least one solvent selected from the groupconsisting of: 1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone,cyclohexanone, 1-hexanol, acetic acid, and mixtures thereof; theviscosity modifier, resin, or binder is present in an amount of about1.0% to 4.5% by weight and comprises at least one viscosity modifier,resin, or binder selected from the group consisting of: polyvinylpyrrolidone, a polyimide, and mixtures thereof; further comprising asecond solvent present in an amount of 0.01% to 5.0% by weight, thesecond solvent comprising an acid or a base; and further comprising athird solvent present in an amount of about 4.5% to 95.4% by weight, thethird solvent comprising at least one solvent selected from the groupconsisting of: cyclohexanol, cyclohexanone, cyclopentanol, butyllactone, and mixtures thereof.

In an additional exemplary composition, the plurality of metallicnanofibers are coated with polyvinyl pyrrolidone and the plurality ofmetallic nanofibers are present in an amount of about 0.01% to 3.0% byweight; the first solvent is present in an amount of about 2.5% to 8.0%by weight and comprises at least one solvent selected from the groupconsisting of: 1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone,cyclohexanone, 1-hexanol, acetic acid, and mixtures thereof; theviscosity modifier, resin, or binder is present in an amount of about1.0% to 4.5% by weight and comprises at least one viscosity modifier,resin, or binder selected from the group consisting of: polyvinylpyrrolidone, a polyimide, and mixtures thereof; further comprising asecond solvent present in an amount of 0.01% to 5.0% by weight, whereinthe second solvent comprises at least one solvent selected from thegroup consisting of: acids, including organic acids such as carboxylicacids, dicarboxylic acids, tricarboxylic acids, alkyl carboxylic acids,acetic acid, oxalic acid, mellitic acid, formic acid, chloroacetic acid,benzoic acid, trifluoroacetic acid, propanoic acid, butanoic acid; basessuch as ammonium hydroxide, sodium hydroxide, potassium hydroxide; andmixtures thereof; and further comprising a third solvent present in anamount of about 4.5% to 95.4% by weight, the third solvent comprising atleast one solvent selected from the group consisting of: cyclohexanol,cyclohexanone, cyclopentanol, butyl lactone, and mixtures thereof.

In another exemplary embodiment, the plurality of metallic nanofibersare coated with polyvinyl pyrrolidone and the plurality of metallicnanofibers are present in an amount of about 0.18% to about 0.3% byweight; the first solvent is present in an amount of about 2.5% to 8.0%by weight and comprises at least one solvent selected from the groupconsisting of: 1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone,cyclohexanone, 1-hexanol, and mixtures thereof; the viscosity modifier,resin, or binder is present in an amount of about 1.0% to 4.5% by weightand comprises at least one viscosity modifier, resin, or binder selectedfrom the group consisting of: polyvinyl pyrrolidone, a polyimide, andmixtures thereof; further comprising a second solvent present in anamount of 0.1% to 2.0% by weight and comprising a carboxylic acid; andfurther comprising a third solvent present in an amount of about 3.7% to96.3% by weight, the third solvent comprising at least one solventselected from the group consisting of: cyclohexanol, cyclohexanone,cyclopentanol, butyl lactone, and mixtures thereof.

In another exemplary composition, the plurality of metallic nanofibersare coated with polyvinyl pyrrolidone and the plurality of metallicnanofibers are present in an amount of about 0.01% to 3.0% by weight;the first solvent is present in an amount of about 2.5% to 8.0% byweight and comprises at least one solvent selected from the groupconsisting of: 1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone,cyclohexanone, 1-hexanol, acetic acid, and mixtures thereof; theviscosity modifier, resin, or binder is present in an amount of about1.0% to 4.5% by weight and is selected from the group consisting of:polyvinyl pyrrolidone, a polyimide, and mixtures thereof; furthercomprising a second solvent present in an amount of 0.01% to 5.0% byweight, wherein the second solvent comprises at least one solventselected from the group consisting of: acids, including organic acidssuch as carboxylic acids, dicarboxylic acids, tricarboxylic acids, alkylcarboxylic acids, acetic acid, oxalic acid, mellitic acid, formic acid,chloroacetic acid, benzoic acid, trifluoroacetic acid, propanoic acid,butanoic acid; bases such as ammonium hydroxide, sodium hydroxide,potassium hydroxide; and mixtures thereof; further comprising a thirdsolvent present in an amount of about 4.5% to 95.4% by weight, the thirdsolvent comprising at least one solvent selected from the groupconsisting of: cyclohexanol, cyclohexanone, cyclopentanol, butyllactone, and mixtures thereof; and wherein the viscosity of thecomposition is substantially between about 200 cps to about 20,000 cpsat 25° C.

In another exemplary composition, the plurality of metallic nanofibersare coated with polyvinyl pyrrolidone and the plurality of metallicnanofibers are present in an amount of about 0.01% to 3.0% by weight;the first solvent is present in an amount of about 18% to 28% by weightand comprises at least one solvent selected from the group consistingof: 1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone, cyclohexanone,1-hexanol, acetic acid, and mixtures thereof; the viscosity modifier,resin, or binder is present in an amount of about 1.4% to 3.75% byweight and comprises at least one viscosity modifier, resin, or binderselected from the group consisting of: polyvinyl pyrrolidone, apolyimide, and mixtures thereof; further comprising a second solventpresent in an amount of 0.001% to 2% by weight, wherein the secondsolvent comprises at least one solvent selected from the groupconsisting of: 1-octanol, acetic acid, diethylene glycol, dipropyleneglycol, propylene glycol, and mixtures thereof; and further comprising athird solvent present in an amount of about 20.4% to 79.6% by weight,the third solvent comprising at least one solvent selected from thegroup consisting of: cyclohexanol, cyclohexanone, cyclopentanol, butyllactone, and mixtures thereof.

In another exemplary embodiment, the viscosity modifier, resin or binderis present in an amount of about 0.75% to 5% by weight and comprises amixture of polyvinyl pyrrolidone and polyvinyl alcohol.

Another exemplary embodiment comprises: a plurality of metallicnanofibers, substantially all of the metallic nanofibers at leastpartially coated with polyvinyl pyrrolidone, the plurality of metallicnanofibers present in an amount of about 0.01% to about 3.0% by weight;a first solvent; a second solvent different from the first solvent; anda viscosity modifier, resin or binder present in an amount of about0.75% to 5.0% by weight and comprises at least one viscosity modifier,resin, or binder selected from the group consisting of: polyvinylpyrrolidone, a polyimide, and mixtures thereof; wherein the viscosity ofthe composition is substantially between about 200 cps to about 20,000cps at 25° C.

In an exemplary embodiment the viscosity modifier, resin or bindercomprises polyvinyl pyrrolidone, the first solvent comprises 1-butanoland the second solvent comprises cyclohexanol. In another exemplaryembodiment, the viscosity modifier, resin or binder comprises apolyimide and is present in an amount of about 0.75% to 5% by weight,and the first solvent comprises cyclohexanone and is present in anamount of about 50 percent to 99.99 percent by weight. In anotherexemplary embodiment, the first solvent comprises cyclohexanone and thesecond solvent comprises a crosslinking agent. In another exemplarycomposition, the viscosity modifier, resin or binder is present in anamount of about 0.75% to 5% by weight and comprises a mixture ofpolyvinyl pyrrolidone and polyvinyl alcohol.

Another exemplary embodiment comprises: a plurality of metallicnanofibers, substantially all of the metallic nanofibers at leastpartially coated with polyvinyl pyrrolidone, the plurality of metallicnanofibers present in an amount of about 0.01% to 3.0% by weight; afirst solvent present in an amount of about 0.01% to 10% by weight andcomprising at least one solvent selected from the group consisting of:1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone, cyclohexanone,1-hexanol, acetic acid, and mixtures thereof; a second solvent presentin an amount of about 1.75% to 98.25% by weight and comprising at leastone solvent selected from the group consisting of: cyclohexanol,cyclohexanone, cyclopentanol, butyl lactone, and mixtures thereof; and aviscosity modifier, resin or binder present in an amount of about 0.75%to 5.0% by weight and comprising at least one viscosity modifier, resin,or binder selected from the group consisting of: polyvinyl pyrrolidone,a polyimide, and mixtures thereof; wherein the viscosity of thecomposition is substantially between about 200 cps to about 20,000 cpsat 25° C.

Various percentages of the constituents and various viscosities of theexemplary compositions are also disclosed.

In an exemplary embodiment, the viscosity modifier, resin, or binder,when dried or cured, forms a polymer or resin lattice or structuresubstantially about the periphery of each metallic nanofiber of theplurality of metallic nanofibers. In an exemplary embodiment, thecomposition is substantially optically transparent when dried or cured.In another exemplary embodiment, the composition has a relativeevaporation rate less than one, wherein the evaporation rate is relativeto butyl acetate having a rate of one.

A method of using the composition is also disclosed, with the methodcomprising: printing the composition to form an electrical contact.

An exemplary apparatus is also disclosed, comprising: a plurality ofmetallic nanofibers embedded in a polymer; wherein the polymer comprisesat least one polymer selected from the group consisting of: polyvinylpyrrolidone, a polyimide, and mixtures thereof.

In an exemplary embodiment, the cured or polymerized resin or polymercomprises polyvinyl pyrrolidone, or a mixture of polyvinyl pyrrolidoneand polyvinyl alcohol. In another exemplary embodiment, the cured orpolymerized resin or polymer comprises a cellulose resin such as hydroxymethylcellulose, methylcellulose, ethyl cellulose, propylmethylcellulose, methoxy cellulose, methoxy methylcellulose, methoxypropyl methylcellulose, hydroxy propyl methylcellulose, carboxymethylcellulose, hydroxy ethylcellulose, or mixtures thereof. In anotherexemplary embodiment, the cured or polymerized resin or polymercomprises a polyimide.

The exemplary apparatus may further comprise: at least a trace amount ofa solvent; and/or at least a trace amount of a viscosity modifier;and/or at least trace amounts of a surfactant.

Numerous other advantages and features of the present invention willbecome readily apparent from the following detailed description of theinvention and the embodiments thereof, from the claims and from theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention will bemore readily appreciated upon reference to the following disclosure whenconsidered in conjunction with the accompanying drawings, wherein likereference numerals are used to identify identical components in thevarious views, and wherein reference numerals with alphabetic charactersare utilized to identify additional types, instantiations or variationsof a selected component embodiment in the various views, in which:

FIG. 1 is a perspective view illustrating an exemplary apparatusembodiment.

FIG. 2 is a cross-sectional view illustrating the exemplary apparatusembodiment.

FIG. 3 is a photograph of an exemplary apparatus embodiment fabricatedwith an exemplary metallic nanofiber ink at a magnification of 880×.

FIG. 4 is a perspective view illustrating an exemplary functionalizedmetallic nanofiber embodiment.

FIG. 5 is a cross-sectional view illustrating an exemplaryfunctionalized metallic nanofiber embodiment.

FIG. 6 is a flow diagram illustrating an exemplary method embodiment formetallic nanofiber ink fabrication.

FIG. 7 is a graphical diagram illustrating sheet resistance and opticaltransmissivity for an exemplary apparatus embodiment fabricated with anexemplary metallic nanofiber ink.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

While the present invention is susceptible of embodiment in manydifferent forms, there are shown in the drawings and will be describedherein in detail specific exemplary embodiments thereof, with theunderstanding that the present disclosure is to be considered as anexemplification of the principles of the invention and is not intendedto limit the invention to the specific embodiments illustrated. In thisrespect, before explaining at least one embodiment consistent with thepresent invention in detail, it is to be understood that the inventionis not limited in its application to the details of construction and tothe arrangements of components set forth above and below, illustrated inthe drawings, or as described in the examples. Methods and apparatusesconsistent with the present invention are capable of other embodimentsand of being practiced and carried out in various ways. Also, it is tobe understood that the phraseology and terminology employed herein, aswell as the abstract included below, are for the purposes of descriptionand should not be regarded as limiting.

Exemplary embodiments of the invention provide a liquid and/or gelsuspension of metallic nanofibers 100 which is capable of being printed,and may be referred to equivalently herein as “metallic nanofiber ink”,it being understood that “metallic nanofiber ink” means and refers to aliquid and/or gel suspension of metallic nanofibers (also referred toequivalently as metallic nanowires), such as exemplary metallicnanofibers 100. An exemplary method of the invention also comprises amethod of manufacturing metallic nanofiber ink which, as discussed ingreater detail below, suspends a plurality of metallic nanofibers 100 inone or more solvents and a viscous resin or polymer mixture which iscapable of being printed, for example, to produce a substantiallytransparent conductor when cured or solidified, such as for themanufacture of LED-based devices and photovoltaic devices, for exampleand without limitation. Exemplary conductors, apparatuses and systemsformed by printing such an exemplary metallic nanofiber ink are alsodisclosed.

The metallic nanofiber ink disclosed herein may be deposited, printed orotherwise applied to any substrate, device, or may be deposited, printedor otherwise applied to any product of any kind or to form any productof any kind, including lighting, photovoltaic panels, electronicdisplays such as computer, television, tablet and mobile devicedisplays, packaging, signage or indicia for product packaging, or as aconductor for any other product or device, such as a consumer product, apersonal product, a business product, an industrial product, anarchitectural product, a building product, etc. The metallic nanofiberink may be printed onto the substrate, device, article, or packagingthereof, as either a functional or decorative component of the article,package, or both. In one embodiment, the metallic nanofiber ink isprinted in the form of indicia and combined with light emitting diodes.In another embodiment, the metallic nanofiber ink is printed to formelectrical contacts for light emitting diodes or photovoltaic diodes. Inanother embodiment, the metallic nanofiber ink is printed to formelectrical contacts for any two, three or more terminal device, such asa transistor or RFID tag. The article or package may be formed from anyconsumer-acceptable material.

For example and without limitation, the metallic nanofiber ink disclosedherein may be utilized to form any of the conductors or conductivelayers, transparent or otherwise, for the apparatuses, methods, andsystems referred to and disclosed in the following U.S. patentapplications, U.S. patents, and PCT patent applications, the entirecontents of each of which are incorporated herein by reference with thesame full force and effect as if set forth in their entireties herein,and with priority claimed for all commonly disclosed subject matter(individually and collectively referred to as the “related patentapplications”): U.S. patent application Ser. No. 13/223,279; U.S. patentapplication Ser. No. 13/223,286; U.S. patent application Ser. No.13/223,289; U.S. patent application Ser. No. 13/223,293; U.S. patentapplication Ser. No. 13/223,294; U.S. patent application Ser. No.13/223,297; U.S. patent application Ser. No. 13/223,302; U.S. patentapplication Ser. No. 12/753,888; U.S. patent application Ser. No.12/753,887; U.S. Pat. No. 7,719,187; U.S. Pat. No. 7,972,031; U.S. Pat.No. 7,992,332; U.S. patent application Ser. No. 12/560,334; U.S. patentapplication Ser. No. 12/560,340; U.S. patent application Ser. No.12/560,355; U.S. patent application Ser. No. 12/560,364; U.S. patentapplication Ser. No. 12/560,371; U.S. patent application Ser. No.13/025,137; U.S. patent application Ser. No. 13/025,138; PCT PatentApplication Serial No. PCT/US2011/50168; PCT Patent Application SerialNo. PCT/US2011/50174.

FIG. 1 is a perspective view illustrating an exemplary substantiallytransparent conductor (or conductive apparatus) 150 embodiment. FIG. 2is a cross-sectional view (through the 20-20′ plane of FIG. 1)illustrating the exemplary substantially transparent conductor (orconductive apparatus) 150. FIG. 3 is a photograph of an exemplarysubstantially transparent conductor (or conductive apparatus) 150Aembodiment. FIG. 4 is a perspective view illustrating an exemplaryfunctionalized metallic nanofiber 100B embodiment. FIG. 5 is across-sectional view (through the 30-30′ plane of FIG. 4) illustratingan exemplary functionalized metallic nanofiber 100B embodiment. Inaddition, referring to FIGS. 1-5, those having skill in the art willalso recognize that the various Figures are for purposes of descriptionand explanation, are not drawn to scale, and further may not illustrateany actual or preferred densities or curvatures of the metallicnanofibers 100; for example and without limitation, both the densitiesand the curvatures of the metallic nanofibers 100 may be considerablygreater than that illustrated in FIGS. 1, 2, 4 and 5, and with variousdensities and percentages in the metallic nanofiber ink described ingreater detail below.

Referring to FIGS. 1-2, the exemplary metallic nanofibers 100 areillustrated as at least partially embedded, primarily, in a polymerizedor cured polymer or resin 110 (discussed in greater detail below), whichto some extent possibly may also include residual or trace amounts ofother components of the metallic nanofiber ink as discussed in greaterdetail below, such as depending upon cure time, to form an exemplary,substantially transparent conductor (or conductive apparatus) 150. Anexemplary conductor (or conductive apparatus) 150 is typically asubstantially transparent conductive film, layer, strip, electrode, wireor conductive line or trace, having any shape or form factor, such asthose illustrated and discussed in the related patent applications,although other conductor (or conductive apparatus) 150 shapes and formfactors are considered equivalent and within the scope of thedisclosure. The substantially transparent conductor (or conductiveapparatus) 150 is illustrated as an exemplary conductive line or wire inFIG. 1. An exemplary apparatus 150A is illustrated in the photograph ofFIG. 3, with exemplary metallic nanofibers 100A having a length on theorder of between about twenty to sixty microns (10μ-60μ) and a diameteron the order of between about twenty to one hundred nanometers (10-120nm).

The substantially transparent conductor (or conductive apparatus) 150may be deposited to have any width and length, with the resulting depthdepending to some extent upon the viscosity of the metallic nanofiberink and the sizes (length and diameters) of the metallic nanofibers 100.Referring to FIG. 2, in exemplary embodiments, the substantiallytransparent conductor (or conductive apparatus) 150, once cured ordried, generally has a substantially thin form factor, generally betweenabout 100 to 300 nm thick (or deep), or more particularly, between about150 to 250 nm thick, or more particularly, between about 175 to 225 nm,or more particularly, on the order of about 200 nm thick when theapplied metallic nanofiber ink has a viscosity on the order of 500 cpsusing metallic nanofibers 100 having a length on the order of betweenabout twenty to sixty microns (10μ-60μ) and a diameter on the order ofbetween about twenty to one hundred nanometers (10-120 nm). As a result,many of the metallic nanofibers 100 become and are at least partiallyexposed on the surfaces of the substantially transparent conductor (orconductive apparatus) 150.

Referring to FIG. 4, exemplary metallic nanofibers 100 may have a widevariety of shapes and sizes, and are generally or roughly cylindricallyor rod-shaped, with any of various cross-sectional shapes (such as ahexagonal rod shape illustrated in FIG. 4), also may be solid or hollow(tubular), and generally having a length dimension substantially greaterthan a diameter dimension (also referred to as anisotropic), i.e., anaspect ratio greater than one. As illustrated in FIG. 4, for example andwithout limitation, an exemplary metallic nanofiber 100B issubstantially hexagonal in diameter (or cross-section), having aplurality of substantially flat sides, and further may have one or morecurvatures along its length dimension, as illustrated. A complete,substantial or at least a partial polymer coating 125 or otherfunctionalization is illustrated in FIG. 4 and in cross-section in FIG.5, as discussed in greater detail below. As mentioned above, in a firstexemplary embodiment, the exemplary metallic nanofibers 100A may have alength on the order of about 10μ to about 100μ and a diameter on theorder of about 10 nm to about 120 nm. More particularly, in variousexemplary embodiments, the lengths and diameters of the metallicnanofibers may vary, for example: the plurality of metallic nanofibersmay have lengths between about 1μ and about 250μ and diameters betweenabout 10 nm and about 500 nm; or more particularly, may have lengthsbetween about 10μ and about 150μ and diameters between about 5 nm andabout 250 nm; or more particularly, may have lengths between about 10μand about 100μ and diameters between about 10 nm and about 100 nm; ormore particularly, may have lengths between about 10μ and about 80μ anddiameters between about 10 nm and about 80 nm; or more particularly, mayhave lengths between about 1μ and about 60μ and diameters between about10 nm and about 200 nm; or more particularly, may have lengths betweenabout 10μ and about 70μ and diameters between about 25 nm and about 60nm; or more particularly, the plurality of metallic nanofibers may havelengths between about 40μ and about 60μ and diameters between about 15nm and about 40 nm and/or have lengths between about 10μ and about 25μand diameters between about 10 nm and about 15 nm

In addition, the selection of the lengths of the metallic nanofibers 100for a metallic nanofiber ink may also depend upon the type of printingto be utilized. For example and without limitation, for screen printing,the lengths of the metallic nanofibers 100 may be selected for the poreor hole size of the screen or mesh, to pass through and not becomecaught in the screen.

In various exemplary embodiment, the plurality of metallic nanofibersmay have an aspect ratio between about 500:1 to 100:1, for example andwithout limitation. In various other exemplary embodiments, theplurality of metallic nanofibers may have an aspect ratio between about400:1 to 200:1; an aspect ratio between about 350:1 to 250:1; and/or anaspect ratio between about 350:1 to 275:1, all also for example andwithout limitation. With the length dimension substantially greater thanthe diameter (or width) dimension, such as having lengths 10 to about6000 times greater than the diameter, the exemplary metallic nanofibers100 have some rigidity but are also flexible, which aids in the creationof electrical contacts with each other to form a conductive film, traceor line, in any form factor, and to facilitate the creation ofelectrical contacts with other system components, such as diodes, asillustrated in the related patent applications, to provide correspondingelectrical connections to these other system components.

The dimensions of the exemplary metallic nanofibers 100 may be measured,for example, using a light microscope (which may also include measuringsoftware). As additional examples, the dimensions of the exemplarymetallic nanofibers 100 may be measured using, for example, a scanningelectron microscope (SEM), or Horiba's LA-920. The Horiba LA-920instrument uses the principles of low-angle Fraunhofer Diffraction andLight Scattering to measure the particle size and distribution in adilute solution of particles, such as when embodied in a metallicnanofiber ink. All particle sizes are measured in terms of their numberaverage particle diameters and lengths, as there may be significantoutliers in the fabrication of metallic nanofibers.

The exemplary metallic nanofibers 100 may be comprised of a wide varietyof materials, and a referred to as “metallic” to indicate substantiallyhigh conductivity. In an exemplary embodiment, metallic nanofibers 100are comprised of one or more metals (e.g., aluminum, copper, silver,gold, nickel, palladium, tin, platinum, lead, zinc, etc.), alone or incombination with each other, such as an alloy, for example and withoutlimitation. Combinations of different types of conductors and/orconductive compounds or materials (e.g., ink, polymer, carbon nanotubes,elemental metal, etc.) may also be utilized to form metallic nanofibers100. Multiple layers and/or types of metal or other conductive materialsmay be combined to form the metallic nanofibers 100.

As illustrated in FIG. 5, the exemplary metallic nanofibers 100 may alsobe functionalized with a wide variety of compounds to aid theirdispersion in a liquid or gel. In an exemplary embodiment, metallicnanofibers 100 are functionalized by having a complete or full coating,a substantial coating, or at least a partial coating 125 of a polymer,including a pyrrolidone polymer such as polyvinyl pyrrolidone (“PVP”) orany other polymer, for example and without limitation, such as tofacilitate dispersion of the metallic nanofibers 100 in the metallicnanofiber ink, also for example.

The exemplary metallic nanofibers 100 may be fabricated using anyfabrication techniques which are known currently or which are developedin the future. Exemplary metallic nanofibers 100, such as silvernanofibers, including metallic nanofibers in a functionalized form withPVP coatings, are commercially available and have been obtained fromseveral suppliers, including NanoGap Subnmparticles of Spain, US and UKand having an office in San Francisco, Calif. USA; Blue Nano Inc. ofCharlotte and Cornelius, N.C. USA; Zhejiang Kechuang Advanced MaterialsTechnology Co. Ltd. of Zhejiang, China; and ACS Material LLC, havingoffices in Medford, Mass. and Ames, Iowa, USA. For example, metallicnanofibers 100 exemplary include AW030 silver fibers obtained fromZhejiang Kechuang Advanced Materials Technology Co. Ltd.

Metallic Nanofiber Ink Example 1

-   -   A composition comprising:    -   a plurality of functionalized metallic nanofibers, substantially        all of the metallic nanofibers having at least a partial coating        of a polymer;    -   a solvent; and    -   a viscosity modifier.

Metallic Nanofiber Ink Example 2

-   -   A composition comprising:    -   a plurality of functionalized metallic nanofibers, substantially        all of the metallic nanofibers having at least a partial coating        of a polymer;    -   a solvating agent; and    -   a viscosity modifier.

Metallic Nanofiber Ink Example 3

-   -   A composition comprising:    -   a plurality of functionalized metallic nanofibers, substantially        all of the metallic nanofibers having at least a partial coating        of a polymer;    -   a wetting or rewetting solvent; and    -   a viscosity modifier.

Metallic Nanofiber Ink Example 4

-   -   A composition comprising:    -   a plurality of functionalized metallic nanofibers, substantially        all of the metallic nanofibers having at least a partial coating        of a polymer;    -   a first solvent;    -   a first viscosity modifier; and    -   a second, adhesion promoting solvent or a second, adhesive        viscosity modifier.

Metallic Nanofiber Ink Example 5

-   -   A composition comprising:    -   a plurality of functionalized metallic nanofibers, substantially        all of the metallic nanofibers having at least a partial coating        of a polymer;    -   a first solvent having a comparatively high melting point and        comprising a solid at room temperature (about 25° C.);    -   a first viscosity modifier;    -   a second, adhesion promoting solvent or a second, adhesive        viscosity modifier; and    -   a third solvent to lower the melting point and liquefy the first        solvent at room temperature (about 25° C.).

Metallic Nanofiber Ink Example 6

-   -   A composition comprising:    -   a plurality of functionalized metallic nanofibers, substantially        all of the metallic nanofibers having at least a partial coating        of a polyvinyl pyrrolidone polymer and having lengths between        about 40μ and about 60μ and diameters between about 25 nm and        about 35 nm;    -   a first solvent having a comparatively high melting point and        comprising a solid at room temperature (about 25° C.);    -   a viscosity modifier;    -   a second, adhesion promoting solvent; and    -   a third solvent to lower the melting point and liquefy the first        solvent at room temperature (about 25° C.).

Metallic Nanofiber Ink Example 7

-   -   A composition comprising:    -   a plurality of functionalized metallic nanofibers, substantially        all of the metallic nanofibers having at least a partial coating        of a polyvinyl pyrrolidone polymer;    -   a first solvent comprising cyclohexanol or cyclohexanone;    -   a viscosity modifier comprising polyvinyl pyrrolidone or a        polyimide;    -   a second, adhesion promoting solvent comprising acetic acid; and    -   a third solvent comprising 1-butanol, n-methylpyrrolidone or        cyclopentanone.

In various exemplary embodiments, such as in Examples 1-7 and theadditional Examples below, a metallic nanofiber ink comprises aplurality of functionalized metallic nanofibers 100, each or most havingat least a partial coating of a polymer such as PVP, and which aredispersed in a solvent (such as cyclohexanol, 1-butanol,n-methylpyrrolidone, cyclohexanone, cyclopentanone, acetic acid,ethanol, 1-pentanol or 1-hexanol) and a viscosity modifier, such as PVP.One or more solvents (as first, second or third solvents) may be usedequivalently, for example and without limitation: water; alcohols suchas methanol, ethanol, N-propanol (including 1-propanol, 2-propanol(isopropanol or IPA), 1-methoxy-2-propanol), butanol (including1-butanol, 2-butanol (isobutanol)), pentanol (including 1-pentanol,2-pentanol, 3-pentanol), hexanol (including 1-hexanol, 2-hexanol,3-hexanol), octanol, N-octanol (including 1-octanol, 2-octanol,3-octanol), tetrahydrofurfuryl alcohol (THFA), cyclohexanol,cyclopentanol, terpineol; lactones such as butyl lactone; ethers such asmethyl ethyl ether, diethyl ether, ethyl propyl ether, and polyethers;ketones, including diketones and cyclic ketones, such as cyclohexanone,cyclopentanone, cycloheptanone, cyclooctanone, acetone, benzophenone,acetylacetone, acetophenone, cyclopropanone, isophorone, methyl ethylketone; esters such ethyl acetate, dimethyl adipate, proplyene glycolmonomethyl ether acetate, dimethyl glutarate, dimethyl succinate,glycerin acetate, carboxylates; glycols such as ethylene glycols,diethylene glycols, polyethylene glycols, propylene glycols, dipropyleneglycols, glycol ethers, glycol ether acetates; carbonates such aspropylene carbonate; glycerols such as glycerin; n-methylpyrrolidone,acetonitrile, tetrahydrofuran (THF), dimethyl formamide (DMF), N-methylformamide (NMF), dimethyl sulfoxide (DMSO); acids, including organicacids such as carboxylic acids, dicarboxylic acids, tricarboxylic acids,alkyl carboxylic acids, acetic acid, oxalic acid, mellitic acid, formicacid, chloroacetic acid, benzoic acid, trifluoroacetic acid, propanoicacid, butanoic acid; bases such as ammonium hydroxide, sodium hydroxide,potassium hydroxide; and mixtures thereof. In addition, a solvent mayalso function as a viscosity modifier and vice-versa, such ascyclohexanol, terpineol and n-methyl pyrrolidone, for example andwithout limitation.

In various exemplary embodiments, the selection of a first (or second)solvent is based upon at least two properties or characteristics. Afirst characteristic of the solvent is its ability be soluble in or tosolubilize a binder, a viscosity modifier or an adhesive viscositymodifier such as PVP, PVA, methoxy cellulose or hydroxy propylmethylcellulose resin. A second characteristic or property is itsevaporation rate, which should be slow enough to allow sufficient screenresidence (for screen printing) of the metallic nanofiber ink or to meetother printing parameters. In various exemplary embodiments, anexemplary evaporation rate is less than one (<1, as a relative ratecompared with butyl acetate), or more specifically, between 0.0001 and0.9999.

One or more viscosity modifiers, binders, resins or thickeners (as aviscosity modifier) may be used, for example and without limitation:polymers (or equivalently, polymeric precursors or polymerizableprecurors) such as polyvinyl pyrrolidone (also referred to or known aspolyvinyl pyrrolidinone), polyvinyl alcohol, polyimide polymers andcopolymers (including aliphatic, aromatic and semi-aromatic polyimides),acrylate and (meth)acrylate polymers and copolymers; glycols such asethylene glycols, diethylene glycol, polyethylene glycols, propyleneglycols, dipropylene glycols, glycol ethers, glycol ether acetates;clays such as hectorite clays, garamite clays, organo-modified clays;saccharides and polysaccharides such as guar gum, xanthan gum;celluloses and modified celluloses such as hydroxy methylcellulose,methylcellulose, ethyl cellulose, propyl methylcellulose, methoxycellulose, methoxy methylcellulose, methoxy propyl methylcellulose,hydroxy propyl methylcellulose, carboxy methylcellulose, hydroxyethylcellulose, ethyl hydroxyl ethylcellulose, cellulose ether,cellulose ethyl ether, chitosan; fumed silica (such as Cabosil), silicapowders and modified ureas such as BYK® 420 (available from BYK ChemieGmbH); and mixtures thereof. As mentioned above, some of the viscositymodifiers may also function as solvents and vice-versa, such as thevarious glycols, and therefore are included in the various listings ofexemplary solvents and viscosity modifiers. In several Examplesdiscussed below, E-3 and E-10 cellulose resins available from The DowChemical Company (www.dow.com) and Hercules Chemical Company, Inc.(www.herchem.com) are utilized. In an exemplary embodiment, the PVPutilized has a molecular weight between about 50,000 to about 3 millionMW, or more particularly between about 100,000 to 2 million MW, or moreparticularly between about 500,000 to 1.5 million MW, or moreparticularly between about 750,000 to 1.25 million MW, while the PVA hasa molecular weight of about 133K, or more generally between about 50,000to 250K MW, and may be obtained from Polysciences, Inc. of Warrington,Pa. USA. Other viscosity modifiers may be used, as well as particleaddition to control viscosity, as described in Lewis et al., PatentApplication Publication Pub. No. US 2003/0091647. Other viscositymodifiers or binders may also be utilized. As mentioned above, themetallic nanofibers 100 are functionalized with a substantial, completeor at least a partial coating of polyvinyl pyrrolidone (PVP) having amolecular weight between about 5,000 to about 50,000 MW.

Referring to Metallic Nanofiber Ink Examples 1-7 and the additionalExamples described below, there are a wide variety of exemplary metallicnanofiber ink compositions within the scope of the present disclosure.Generally, as in Example 1, a liquid suspension of metallic nanofibers100 comprises a plurality of functionalized metallic nanofibers 100, afirst solvent (such as 1-butanol, ethanol, 1-pentanol,n-methylpyrrolidone, cyclohexanone, 1-hexanol, acetic acid, or othersolvents discussed herein), which also may be an adhesion promotingsolvent as in Examples 5-7, and a viscosity modifier, resin or binder(such those discussed above, which may also be an adhesive viscositymodifier, resin or binder as in Example 5); and as in Examples 2 and 3,a liquid suspension of metallic nanofibers 100 comprises a plurality offunctionalized metallic nanofibers 100, a solvating agent or a wettingor rewetting solvent (such as one of the second solvents discussedherein), and a viscosity modifier, resin or binder. More particularly,such as in Examples 4-7, a liquid suspension of metallic nanofibers 100comprises a plurality of functionalized metallic nanofibers 100, a firstsolvent (such as 1-butanol, ethanol, 1-pentanol, n-methylpyrrolidone,cyclohexanone, 1-hexanol, or acetic acid), a viscosity modifier, resinor binder (or equivalently, a viscous compound, a viscous resin, aviscous agent, a viscous polymer, a viscous resin, a viscous binder, athickener, and/or a rheology modifier) such as PVP or a polyimide, and asecond, adhesion promoting solvent or a second, adhesive viscositymodifier, to provide a metallic nanofiber ink having a viscosity betweenabout 100 centipoise (cps) and 20,000 cps at room temperature (about 25°C.), or more preferably between about 200-1000 centipoise (cps) cps atroom temperature (about 25° C.), or more preferably between about400-600 centipoise (cps) cps at room temperature (about 25° C.) for ascreen printable ink (or between about 500 cps to 60,000 cps at arefrigerated temperature (e.g., 5-10° C.)). Depending upon theviscosity, the resulting composition may be referred to equivalently asa liquid or as a gel suspension of metallic nanofibers, and anyreference to liquid or gel herein shall be understood to mean andinclude the other.

In addition, the resulting viscosity of the metallic nanofiber ink willgenerally vary depending upon the type of printing process to beutilized and may also vary depending upon the metallic nanofibercomposition and size. For example, a metallic nanofiber ink for screenprinting may have a viscosity between about 100 centipoise (cps) and25,000 cps at room temperature, or more specifically between about 200centipoise (cps) and 5,000 cps at room temperature, or more specificallybetween about 200 centipoise (cps) and 1,000 cps at room temperature, ormore specifically between about 300 centipoise (cps) and 800 cps at roomtemperature, or more specifically between about 400 centipoise (cps) and600 cps at room temperature, or more specifically between about 450centipoise (cps) and 550 cps at room temperature. Also for example, ametallic nanofiber ink for flexographic printing may have a viscositybetween about 100 centipoise (cps) and 10,000 cps at room temperature,or more specifically between about 200 centipoise (cps) and 4,000 cps atroom temperature, or more specifically between about 500 centipoise(cps) and 3,000 cps at room temperature, or more specifically betweenabout 1,800 centipoise (cps) and 2,200 cps at room temperature, or morespecifically between about 2,000 centipoise (cps) and 6,000 cps at roomtemperature, or more specifically between about 2,500 centipoise (cps)and 4,500 cps at room temperature, or more specifically between about2,000 centipoise (cps) and 4,000 cps at room temperature.

Viscosity may be measured in a wide variety of ways. For purposes ofcomparison, the various specified and/or claimed ranges of viscosityherein have been measured using a Brookfield viscometer (available fromBrookfield Engineering Laboratories of Middleboro, Mass., USA) at ashear stress of about 200 pascals (or more generally between 190 and 210pascals), in a water jacket at about 25° C., using a spindle SC4-27 at aspeed of about 10 rpm (or more generally between 1 and 30 rpm,particularly for refrigerated fluids, for example and withoutlimitation).

Referring to Metallic Nanofiber Ink Examples 4-7, the liquid suspensionof metallic nanofibers 100 may further comprise a second, adhesionpromoting solvent or a second, adhesive viscosity modifier, namely, anyof the solvents or viscosity modifiers mentioned above which have theadditional property of adhesion promotion, including modification of asubstrate surface to allow or promote adherence of the metallicnanofiber ink and resulting film or trace (150). Such an adhesionpromoting solvent or adhesive viscosity modifier may provide for any ofthe following: adhering the metallic nanofibers 100 to another conductor(e.g., a diode contact); adhering the film or trace (150) to a substrate(e.g., during device fabrication (e.g., printing)) such as plastic,glass, silicon, polyethylene terephthalates (PET), polycarbonate,polymethyl methacrylate (PMMA), etc.; and/or an infrastructure (e.g.,polymeric) (when dried or cured) for holding the metallic nanofibers 100in place in an apparatus (150, 150A). While providing such adhesion,such a viscosity modifier, resin or binder should also have somecapability to de-wet from inter-fiber contacts of the metallicnanofibers 100 to each other (i.e. to de-wet from the contact pointsbetween the various metallic nanofibers 100) and thereby help todecrease the sheet resistance of the apparatus 150. Such adhesive,viscosity and de-wetting properties are among the reasons methoxylcellulose or other cellulose resins have been utilized in variousexemplary embodiments. In addition, such adhesion promoting to asubstrate is also a reason a solvent such as acetic acid (or anotheracid or base) may be utilized in exemplary embodiments. Other suitableviscosity modifiers or binders may also be selected empirically.

Additional properties of the viscosity modifier, resin or binder arealso useful and within the scope of the disclosure. First, such aviscosity modifier, resin or binder should prevent the suspendedmetallic nanofibers 100 from settling out or prevent hard caking of themetallic nanofibers 100 at a selected temperature, and potentiallyfurther allow comparatively easy redispersion of the metallic nanofibers100 with minor agitation or stirring. Second, such a viscosity modifier,resin or binder should aid in printing the metallic nanofibers 100 in auniform manner during apparatus (150, 150A) fabrication. Third, theviscosity modifier, resin or binder may also serve to cushion orotherwise protect the metallic nanofibers 100 during the printingprocess.

Referring to Examples 2-7, the liquid suspension of metallic nanofibers100 may further comprise a second solvent (Examples 4-7) or a solvatingagent or a wetting solvent (Examples 2 and 3), with many examplesdiscussed in greater detail below. Such a (first or second) solvent isselected as a wetting (equivalently, solvating) or rewetting agent oradhesion promoting for facilitating ohmic or electrical contact betweenmetallic nanofibers 100 and other devices, such as diodes ortransistors, and between the metallic nanofibers 100 themselves, alsofor example and without limitation.

The balance of the liquid or gel suspension of metallic nanofibers 100is generally another, second solvent, such as cyclohexanol,cyclohexanone, cyclopentanone and/or a third solvent (or fourth or moresolvents), such as 1-butanol, n-methylpyrrolidone, or deionized water,and any descriptions of percentages herein shall assume that the balanceof the liquid or gel suspension of metallic nanofibers 100 is such asecond, third or fourth solvent such as cyclohexanol, cyclohexanone,cyclopentanone, n-methylpyrrolidone, 1-butanol or water, and alldescribed percentages are based on weight, rather than volume or someother measure. It should also be noted that the various metallicnanofiber ink suspensions may all be mixed in a typical atmosphericsetting, without requiring any particular composition of air or othercontained or filtered environment.

Solvent selection may also be based upon the polarity of the solvent. Inan exemplary embodiment, a first solvent such as an alcohol may beselected as a polar or hydrophilic solvent, to facilitate de-wetting offof the metallic nanofibers 100 and other conductors during apparatus150, 150A, fabrication, while concomitantly being able to be soluble inor solubilize a viscosity modifier.

Another useful property of an exemplary metallic nanofiber ink is thatthe dried or cured metallic nanofiber ink is substantially clear atvisible wavelengths, to substantially allow or not interfere with theemission of visible light generated by devices such as LEDs. Varioustransmissivity percentages and corresponding sheet resistances fordifferent densities of metallic nanofibers 100 are provided in Table Ibelow and illustrated in FIG. 7.

Another way to characterize an exemplary metallic nanofiber ink is basedupon the size of the metallic nanofibers 100, as discussed above. Asillustrated in Example 6, the metallic nanofibers 100 generally may bebetween about 40-60 microns in length, and have a diameter between about25 nm to about 35 nm. Additional size ranges also may be provided aspreviously discussed.

The metallic nanofiber ink may also be characterized by its electricalproperties. For example, the metallic nanofibers 100 may be suspended inat least one substantially non-insulating carrier or solvent, incontrast with an insulating binder, for example.

Metallic Nanofiber Ink Example 8

-   -   A composition comprising:    -   a plurality of metallic nanofibers, substantially all of the        metallic nanofibers having at least a partial coating of        polyvinyl pyrrolidone;    -   a first solvent comprising about 1% to 10% 1-butanol, ethanol,        1-pentanol, n-methylpyrrolidone, 1-hexanol, or acetic acid, or        mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 0.75% to        5.0% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof; and with the balance comprising a second solvent such        as cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol,        butyl lactone, or mixtures thereof.

Metallic Nanofiber Ink Example 9

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer;    -   a first solvent comprising about 2.5% to 8% 1-butanol, ethanol,        1-pentanol, n-methylpyrrolidone, 1-hexanol, or acetic acid, or        mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 1.0% to        4.5% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof; and    -   with the balance comprising a second solvent such as        cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol,        butyl lactone, or mixtures thereof.

Metallic Nanofiber Ink Example 10

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer;    -   a first solvent comprising about 2.5% to 8% 1-butanol, ethanol,        1-pentanol, n-methylpyrrolidone, or 1-hexanol, or mixtures        thereof;    -   a second solvent comprising about 0.01% to 5% of an acid or        base, or mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 1.0% to        4.5% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof; and    -   with the balance comprising a third solvent such as        cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol,        butyl lactone, or mixtures thereof.

Metallic Nanofiber Ink Example 11

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer;    -   a first solvent comprising about 2.5% to 8% of a first alcohol;    -   a second solvent comprising about 0.01% to 5% of an acid or        base, or mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 1.0% to        4.5% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof; and    -   with the balance comprising a second alcohol different from the        first alcohol.

Metallic Nanofiber Ink Example 12

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer;    -   a first solvent comprising about 2.5% to 8% 1-butanol, ethanol,        1-pentanol, n-methylpyrrolidone, or 1-hexanol, or mixtures        thereof;    -   a second solvent comprising about 0.01% to 5% of an acid or        bases, including organic acids such as carboxylic acids,        dicarboxylic acids, tricarboxylic acids, alkyl carboxylic acids,        acetic acid, oxalic acid, mellitic acid, formic acid,        chloroacetic acid, benzoic acid, trifluoroacetic acid, propanoic        acid, butanoic acid, or bases such as ammonium hydroxide, sodium        hydroxide, potassium hydroxide, or mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 1.0% to        4.5% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof; and    -   with the balance comprising a third solvent such as        cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol,        butyl lactone, or mixtures thereof.

Metallic Nanofiber Ink Example 13

-   -   A composition comprising:    -   about 0.18% to 0.3% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer;    -   about 2.5% to 8% of 1-butanol;    -   about 0.1% to 2% of acetic acid;    -   about 1.0% to 4.5% polyvinyl pyrrolidone; and    -   with the balance comprising cyclohexanol, cyclohexanone,        cyclopentanone, cyclopentanol, or butyl lactone, or mixtures        thereof.

Metallic Nanofiber Ink Example 14

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers;    -   a first solvent comprising about 3% to 28% 1-butanol, ethanol,        1-pentanol, n-methylpyrrolidone, or 1-hexanol, or mixtures        thereof;    -   a viscosity modifier, resin, or binder comprising about 1.4% to        3.75% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof; and    -   with the balance comprising a second solvent such as        cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol,        butyl lactone, or mixtures thereof.

Metallic Nanofiber Ink Example 15

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers;    -   a first solvent comprising about 3.0% to 7% 1-butanol, ethanol,        1-pentanol, n-methylpyrrolidone, 1-hexanol, or acetic acid, or        mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 1.4% to        3.75% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof;    -   a second solvent comprising about 0.001% to 2% of 1-octanol,        acetic acid, diethylene glycol, dipropylene glycol, propylene        glycol, potassium hydroxide or sodium hydroxide, or mixtures        thereof; and    -   with the balance comprising a third solvent such as        cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol,        butyl lactone, or mixtures thereof.

Metallic Nanofiber Ink Example 16

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers;    -   a first solvent comprising about 2.5% to 28% 1-butanol, ethanol,        1-pentanol, 1-hexanol, acetic acid, 2-propanol (isopropyl        alcohol or IPA), 1-methoxy-2-propanol, diethylene glycol, or        mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 0.05% to        5.0% cellulose resin such as hydroxy methylcellulose,        methylcellulose, ethyl cellulose, propyl methylcellulose,        methoxy cellulose, methoxy methylcellulose, methoxy propyl        methylcellulose, hydroxy propyl methylcellulose, carboxy        methylcellulose, hydroxy ethylcellulose, ethyl hydroxyl        ethylcellulose, or mixtures thereof;    -   a second solvent comprising about 5% to 50% of n-propanol,        2-propanol, propylene glycol, or diethylene glycol, or mixtures        thereof; and    -   with the balance comprising a third solvent such as        1-methoxy-2-propanol, cyclohexanol, cyclohexanone,        cyclopentanone, cyclopentanol, butyl lactone, or mixtures        thereof.

Metallic Nanofiber Ink Example 17

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers 100;    -   a first solvent comprising about 18% to 28% 2-propanol        (isopropyl alcohol or IPA), 1-methoxy-2-propanol, 1-butanol,        ethanol, diethylene glycol, 1-pentanol or 1-hexanol, or mixtures        thereof;    -   a viscosity modifier, resin, or binder comprising about 1.5% to        2.5% cellulose resin such as propoxymethyl cellulose, methoxyl        cellulose or hydroxypropyl cellulose resin, or mixtures thereof;    -   a second solvent comprising about 15% to 25% of n-propanol,        2-propanol, or diethylene glycol, or mixtures thereof; and    -   with the balance comprising a third solvent such as (deionized)        water, 1-methoxy-2-propanol, cyclohexanol, cyclohexanone,        cyclopentanone, cyclopentanol, butyl lactone, or mixtures        thereof.

Metallic Nanofiber Ink Example 18

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers 100;    -   a first solvent comprising about 2.0% to 10.0%        n-methylpyrrolidone, 2-propanol (isopropyl alcohol or IPA),        1-methoxy-2-propanol, 1-butanol, ethanol, diethylene glycol,        1-pentanol, n-methylpyrrolidone, or 1-hexanol, or mixtures        thereof;    -   a first viscosity modifier, resin, or binder comprising about        0.75% to 5.0% PVP, polyvinyl alcohol, or a polyimide, or        mixtures thereof;    -   a second viscosity modifier, resin, or binder comprising about        7% to 12% alpha-terpineol;    -   a second solvent comprising about 1% to 5% of n-propanol,        2-propanol, or diethylene glycol, or mixtures thereof; and    -   with the balance comprising a third solvent such as        n-methylpyrrolidone, cyclohexanol, cyclohexanone,        cyclopentanone, cyclopentanol, butyl lactone, or mixtures        thereof.

Metallic Nanofiber Ink Example 19

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers 100;    -   a first solvent comprising about 18% to 28% n-methyl        pyrrolidone, 2-propanol (isopropyl alcohol or IPA),        1-methoxy-2-propanol, 1-butanol, ethanol, diethylene glycol,        1-pentanol, n-methylpyrrolidone, or 1-hexanol, or mixtures        thereof;    -   a first viscosity modifier, resin, or binder comprising about        0.75% to 5.0% PVP, polyvinyl alcohol (PVA), or a polyimide, or        mixtures thereof (e.g., about 60% PVA with 40% PVP or about 80%        PVA with 20% PVP in n-methyl pyrrolidone); and    -   with the balance comprising a second solvent such as n-methyl        pyrrolidone, cyclohexanol, cyclohexanone, cyclopentanone,        cyclopentanol, butyl lactone, or mixtures thereof.

Metallic Nanofiber Ink Example 20

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer;    -   a first solvent comprising about 2.5% to 8% 1-butanol, ethanol,        1-pentanol, n-methylpyrrolidone, or 1-hexanol, or mixtures        thereof;    -   a second solvent comprising about 0.01% to 5% of acetic acid,        nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric        acid, ammonium hydroxide, sodium hydroxide, or potassium        hydroxide, or mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 1.0% to        4.5% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof; and    -   with the balance comprising a third solvent such as        cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol,        butyl lactone, or mixtures thereof;    -   wherein the viscosity of the composition is substantially        between about 200 cps to about 20,000 cps at 25° C.

Metallic Nanofiber Ink Example 21

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer        and having lengths between about 40μ and about 60μ and diameters        between about 25 nm and about 35 nm;    -   a plurality of metallic particles about 20-30 nm in any        dimension;    -   a first solvent comprising about 2.5% to 8% 1-butanol, ethanol,        1-pentanol, n-methylpyrrolidone, or 1-hexanol, or mixtures        thereof;    -   a second solvent comprising about 0.01% to 5% of an acid or        base, or mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 1.0% to        4.5% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof; and    -   with the balance comprising a third solvent such as        cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol,        butyl lactone, or mixtures thereof.

Metallic Nanofiber Ink Example 22

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer;    -   a plurality of carbon nanotubes;    -   a first solvent comprising about 2.5% to 8% 1-butanol, ethanol,        1-pentanol, n-methylpyrrolidone, or 1-hexanol, or mixtures        thereof;    -   a second solvent comprising about 0.01% to 5% of acetic acid,        nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric        acid, ammonium hydroxide, sodium hydroxide, or potassium        hydroxide, or mixtures thereof;    -   a viscosity modifier, resin, or binder comprising about 1.0% to        4.5% PVP, polyvinyl alcohol, or a polyimide, or mixtures        thereof; and    -   with the balance comprising a third solvent such as        cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol,        butyl lactone, or mixtures thereof.

Metallic Nanofiber Ink Example 23

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer;    -   about 0.5% to 5.0% polyimide; and    -   with the balance comprising a ketone, including diketones and        cyclic ketones, such as cyclohexanone, cyclopentanone,        cycloheptanone, cyclooctanone, acetone, benzophenone,        acetylacetone, acetophenone, cyclopropanone, isophorone, methyl        ethyl ketone, or mixtures thereof.

Metallic Nanofiber Ink Example 24

-   -   A composition comprising:    -   about 0.01% to 3.0% of a plurality of functionalized metallic        nanofibers, substantially all of the metallic nanofibers having        at least a partial coating of a polyvinyl pyrrolidone polymer;    -   about 1.0% to 4.5% polyimide; and    -   with the balance comprising cyclohexanone.

Referring to Metallic Nanofiber Ink Examples 8-24, in an exemplaryembodiment, a plurality of (functionalized) metallic nanofibers 100 aresuspended in a first solvent, such as 1-butanol, ethanol, 1-pentanol,1-hexanol, 2-propanol (isopropyl alcohol or IPA), 1-methoxy-2-propanol,cyclohexanol, cyclohexanone, cyclopentanone, cyclopentanol, butyllactone, diethylene glycol, or n-methyl pyrrolidone, other solventsdiscussed above, or mixtures thereof, such that the functionalizedmetallic nanofibers 100 typically comprise between about 3% to 10% byweight of this intermediate mixture, e.g., 4% to 5% by weight metallicnanofibers 100 suspended in a solvent mixture comprising about 80%cyclohexanol and about 20% 1-butanol. A first or second solvent may thenbe added to further reduce the percentage (by weight) of functionalizedmetallic nanofibers 100 by about 50-75%, to between about 0.01% to 3.0%functionalized metallic nanofibers 100. A third solvent such as aceticacid may also be added. A viscosity modifier, resin or binder comprisingabout 1.0% to 8.5% PVP, polyvinyl alcohol, or a polyimide is dissolvedin a first or second solvent (such as cyclohexanol, cyclohexanone,cyclopentanone, cyclopentanol, butyl lactone, 1-butanol, ethanol,1-pentanol or 1-hexanol, other viscosity modifiers, resins or bindersdiscussed above, or mixtures thereof), typically at 80-90° C. with animpeller or stirring bead, then allowed to cool to room temperature.(For consistency between batches, the PVP is typically heated anddessicated prior to use, and is reflected in all PVP weight percentagesdescribed herein). The metallic nanofibers 100 in the first (or second)solvent are then added to the viscosity modifier, resin or bindermixture, mixing with a helical impeller for 3 to 10 minutes, dependingon the batch size, at a moderate speed to avoid damaging the metallicnanofibers 100, at standard atmospheric pressure and at room temperature(about 25° C.), which further serves to avoid any harm or damage to thePVP functionalization of the metallic nanofibers 100.

A particular advantage of this formulation using cyclohexanol and1-butanol is that the various percentages of metallic nanofibers 100 andsolvents such as 1-butanol may be adjusted independently of the other.

The viscosity modifier, resin or binder provides sufficient viscosityfor the metallic nanofibers 100 that they are substantially maintainedin suspension and do not settle out of the liquid or gel suspension,particularly under refrigeration.

A second or third (or fourth) solvent such as deionized water also maybe added, to adjust the relative percentages and reduce viscosity, asmay be necessary or desirable. In addition, other first, second or thirdsolvents which may be utilized equivalently include, for example andwithout limitation, water; alcohols such as methanol, ethanol,N-propanol (including 1-propanol, 2-propanol (isopropanol or IPA),1-methoxy-2-propanol), butanol (including 1-butanol, 2-butanol(isobutanol)), pentanol (including 1-pentanol, 2-pentanol, 3-pentanol),hexanol (including 1-hexanol, 2-hexanol, 3-hexanol), octanol, N-octanol(including 1-octanol, 2-octanol, 3-octanol), tetrahydrofurfuryl alcohol(THFA), cyclohexanol, cyclopentanol, terpineol; lactones such as butyllactone; ethers such as methyl ethyl ether, diethyl ether, ethyl propylether, and polyethers; ketones, including diketones and cyclic ketones,such as cyclohexanone, cyclopentanone, cycloheptanone, cyclooctanone,acetone, benzophenone, acetylacetone, acetophenone, cyclopropanone,isophorone, methyl ethyl ketone; esters such ethyl acetate, dimethyladipate, proplyene glycol monomethyl ether acetate, dimethyl glutarate,dimethyl succinate, glycerin acetate, carboxylates; glycols such asethylene glycols, diethylene glycols, polyethylene glycols, propyleneglycols, dipropylene glycols, glycol ethers, glycol ether acetates;carbonates such as propylene carbonate; glycerols such as glycerin;n-methylpyrrolidone, acetonitrile, tetrahydrofuran (THF), dimethylformamide (DMF), N-methyl formamide (NMF), dimethyl sulfoxide (DMSO);acids, including organic acids such as carboxylic acids, dicarboxylicacids, tricarboxylic acids, alkyl carboxylic acids, acetic acid, oxalicacid, mellitic acid, formic acid, chloroacetic acid, benzoic acid,trifluoroacetic acid, propanoic acid, butanoic acid; bases such asammonium hydroxide, sodium hydroxide, potassium hydroxide; and mixturesthereof.

While generally the various metallic nanofiber inks are mixed in theorder described above, it should also be noted that the various firstsolvent, viscosity modifier, second solvent, and third solvent (such aswater) may be added or mixed together in other orders, any and all ofwhich are within the scope of the disclosure.

Additional surfactants or non-foaming agents for printing may beutilized as an option, but are not required for proper functioning andexemplary printing.

FIG. 6 is a flow diagram illustrating an exemplary method embodiment formanufacturing metallic nanofiber ink, and provides a useful summary. Themethod begins, start step 200, with suspending or dispersing themetallic nanofibers 100 in a first solvent, step 205. A viscositymodifier or binder is then dissolved or mixed with a first or secondsolvent, step 210, heating as necessary or desirable, followed bycooling to room temperature (about 25° C.). The method then adds themetallic nanofibers 100 in the first solvent to the mixture of theviscosity modifier or binder and first or second solvent, step 215. Anyweight percentages may be adjusted using a first, second or thirdsolvent such as deionized water, step 220. In step 225, the method thenmixes the plurality of metallic nanofibers 100, first solvent, viscositymodifier or binder, second solvent, and any additional first, second orthird solvents for about 3-10 minutes at room temperature (about 25° C.)in an air atmosphere, with a resulting viscosity between about 200 cpsto about 25,000 cps, e.g., 500 cps for screen printing. The method maythen end, return step 230. It should also be noted that steps 205, 210,and 220 may occur in other orders, as described above, and may berepeated as needed, and that optional, additional mixing steps may alsobe utilized.

Additional components may also be included in the metallic nanofiberink, such as CNTs or particulate materials. For example, in theembodiment of Example 21, metallic particles have also been added, suchas silver nanoparticles having a size on the order of about 20-30 nm inany dimension, such as substantially spherical or oblong, available as010 nanosilver from Ink Tec of Korea. When such particles are alsoincluded, the printed film (discussed below) may also be sintered aspart of the curing process at about 130° C. to couple the particles tothe metallic nanofibers 100. Also for example, in the embodiment ofExample 22, carbon nanotubes have also been added, such as carbonnanotubes in a liquid carrier available from SouthWest NanoTechnologies,Inc., Norman, Okla., USA. It should be noted that for added robustness,the various cured metallic nanofiber inks of the Examples may beoverprinted with a stabilizing uv curable sealant of polymer asdiscussed below.

Dried or Cured Metallic Nanofiber Ink Example 1

-   -   A composition comprising:    -   a plurality of metallic nanofibers 100; and    -   a cured or polymerized resin or polymer.

Dried or Cured Metallic Nanofiber Ink Example 2

-   -   A composition comprising:    -   a plurality of metallic nanofibers 100;    -   a cured or polymerized resin or polymer; and    -   at least trace amounts of a solvent.

Dried or Cured Metallic Nanofiber Ink Example 3

-   -   A composition comprising:    -   a plurality of metallic nanofibers 100;    -   a cured or polymerized resin or polymer;    -   at least trace amounts of a solvent; and    -   at least trace amounts of a surfactant.

The metallic nanofiber ink may then be deposited in any pattern (e.g, asa sheet, conformal coating, lines or wires), such as through printing,to a wet film thickness of about 4μ-25μ, depending upon the type ofprinting or other deposition (such as screen or flexographic printing),and more preferably to about 16μ, such as through screen printing usinga 280-500 mesh polyester, or PTFE-coated, or stainless steel screenhaving open areas large enough to permit substantially free passage ofthe longer metallic nanofibers 100 through the screen, and the volatileor evaporative components are dissipated, such as through a heating, uvcure, a radiation cure, or any drying process, for example and withoutlimitation, to leave the metallic nanofibers 100 in the cured orpolymerized resin or polymer. Depending upon the selected viscositymodifier, resin or polymer, curing of a polymer or polymerization of apolymer precursor may occur, and additionally may be crosslinked, suchas by the addition of a crosslinking agent in the various exemplarycompositions.

In an exemplary embodiment, the wet film is then cured or polymerized byheating for about 4-6 minutes, using a ramp cure, starting at about 65°C. to about 140-160° C., such as up to about 150° C. During such curingat these temperatures and with the exemplary combinations of solventsdescribed above (e.g., cyclohexanol, cyclohexanone, cyclopentanone,1-butanol, n-methylpyrrolidone), the PVP functionalization of themetallic nanofibers 100 dewets or pulls away from the metallicnanofibers 100, such that a sufficient number of the metallic nanofibers100 form direct contacts with each other to form a conductive mesh andprovide for sufficient conductivity at the various sheet resistancesdiscussed and illustrated in Table 1 below, and further provide forelectrical contacts with other system components, both generally withoutintervening or sandwiched PVP or other interference from the PVP coatingon the metallic nanofibers 100. As a further consequence, the apparatus150 does not require further processing, such as compression through niprollers, to be sufficiently conductive with comparatively low sheetresistance while maintaining substantial transparency. The remainingdried or cured metallic nanofiber ink, as in Dried or Cured MetallicNanofiber Ink Example 1, generally comprises a plurality of metallicnanofibers 100 and a cured or polymerized resin or polymer (which, asmentioned above, generally secures or holds the metallic nanofibers 100in place). While the volatile or evaporative components (such as firstand/or second solvents and/or surfactants) are substantially dissipated,trace or more amounts may remain, as illustrated in Dried or CuredMetallic Nanofiber Ink Examples 2 and 3. As used herein, a “traceamount” of an ingredient should be understood to be an amount greaterthan zero and less than or equal to 5% of the amount of the ingredientoriginally present in the metallic nanofiber ink when initiallydeposited.

Several novel, highly beneficial and synergistic effects have beenempirically observed using the formulations of Examples 7-13 whencyclohexanol is used as a solvent and a comparatively high molecularweight PVP is utilized as the viscosity modifier, resin, or binder(e.g., 750,000 to 1.25 million MW). First, the use of cyclohexanol inthe metallic nanofiber ink does not dissolve or otherwise remove thecomparatively lower molecular weight PVP coating (functionalization)from the metallic nanofibers 100 at room temperature, but also doesmaintain the higher molecular weight PVP polymer in solution at roomtemperature. This promotes a long shelf life of the metallic nanofiberink, as the PVP coating (functionalization) on the metallic nanofibers100 serves to prevent the metallic nanofibers 100 from agglomerating,allowing comparatively easy redispersion after any settling duringstorage of the the metallic nanofiber ink, such as simply shaking theink bottle or other container.

Second, at the elevated temperatures described above for curing thedeposited metallic nanofiber ink, the cyclohexanol in the metallicnanofiber ink does dissolve or otherwise remove the comparatively lowermolecular weight PVP coating (functionalization) from the metallicnanofibers 100, allowing the metallic nanofibers 100 to make directcontact with each other, without any intervening PVP, and therebyreducing the sheet resistance of the apparatus 150, 150A. Third, thecyclohexanol also helps to reduce or remove oxide formation on thesurfaces of the metallic nanofibers 100, also enhancing the quality ofthe contacts of the metallic nanofibers 100 with each other. Fourth,during the cure process described above, the cured PVP (as the viscositymodifier, resin, or binder) tends to force the metallic nanofibers 100together, also enhancing the inter-fiber contacts and reducing the sheetresistance of the apparatus 150, 150A.

The cured metallic nanofiber ink (forming an apparatus 150, 150A)results in a dried film thickness of between about 80 nm to about 300nm, such as about 200 nm. For thicker optically transmissive, conductivefilms (150, 150A), additional layers of metallic nanofiber ink may beoverprinted or otherwise deposited. An exemplary resistivity is about15-60 ohms/square, with optical transmissivity from about 93% to overabout 97%, depending on the formulation, with a higher percentage ofmetallic nanofibers 100 decreasing resistance but also decreasingoptical transmissivity, as illustrated in Table 1, below. A graph ofresistivity versus transmissivity is illustrated in FIG. 7, using theseformulations based on Example 13, the AW030 metallic nanofibersmentioned above, and deposited using screen printing with a 305 mesh. Itshould be noted that the haze data in Table 1 is based upon a linearmodel model fit to measured haze data (rather than the actual or rawhaze data).

TABLE 1 Metallic Optical Nanofibers Optical Ohms/square Density % WeightTransmissivity % Haze % 5 0.103 0.94 78.8 29.7 10 0.056 0.51 87.9 16.420 0.032 0.29 92.9 9.2 30 0.024 0.22 94.6 6.7 40 0.020 0.18 95.5 5.5 500.018 0.16 96.0 4.7 60 0.016 0.15 96.3 4.2 70 0.015 0.14 96.6 3.8 800.014 0.13 96.8 3.6 90 0.014 0.12 96.9 3.4 100 0.013 0.12 97.0 3.2 1500.012 0.10 97.4 2.7 200 0.011 0.10 97.6 2.4 400 0.010 0.09 97.8 2.0 8000.009 0.09 98.0 1.8

As mentioned above, metallic nanofibers 100 may also be sonicated tobreak longer metallic nanofibers 100 into shorter metallic nanofibers100. The resulting mixture of metallic nanofibers 100 having longer andshorter metallic nanofibers 100 may be utilized to produce better andmore flexible surface coverage, and improve electrical contacts withother devices, such as diodes, for example.

The resulting substantially optically transmissive, conductive film,illustrated as apparatus 150, 150, typically comprises the metallicnanofibers 100 embedded in a binder, resin or polymer (resulting fromthe curing of the viscosity modifier, resin or binder), such as metallicnanofibers 100 embedded or emeshed with PVP, PVA or a polyimide,potentially also with residual or trace amounts of the other metallicnanofiber ink components, such as the various solvents or otheradditives mentioned above. The optically transmissive, conductive film(150, 150A) may then be overprinted as necessary or desirable, such asprinting or deposition of additional layers or features, such asphosphors, stabilization or sealing layers (e.g., DuPont 5018 or Nazdar3529 polymers), or other components, as discussed in greater detailbelow and in the related applications.

Any types of deposition processes may be utilized. As a consequence, asused herein, “deposition” includes any and all printing, coating,rolling, spraying, layering, sputtering, plating, spin casting (or spincoating), vapor deposition, lamination, affixing and/or other depositionprocesses, whether impact or non-impact, known in the art. “Printing”includes any and all printing, coating, rolling, spraying, layering,spin coating, lamination and/or affixing processes, whether impact ornon-impact, known in the art, and specifically includes, for example andwithout limitation, screen printing, inkjet printing, electro-opticalprinting, electroink printing, photoresist and other resist printing,thermal printing, laser jet printing, magnetic printing, pad printing,flexographic printing, hybrid offset lithography, Gravure and otherintaglio printing, for example. All such processes are considereddeposition processes herein and may be utilized. The exemplarydeposition or printing processes do not require significantmanufacturing controls or restrictions. No specific temperatures orpressures are required. Some clean room or filtered air may be useful,but potentially at a level consistent with the standards of knownprinting or other deposition processes. For consistency, however, suchas for proper alignment (registration) of the various successivelydeposited layers forming the various embodiments, relatively constanttemperature (with a possible exception, discussed below) and humiditymay be desirable. In addition, the various compounds utilized may becontained within various polymers, binders or other dispersion agentswhich may be heat-cured or dried, air dried under ambient conditions, orIR or uv cured.

It should also be noted, generally for any of the applications ofvarious compounds herein, such as through printing or other deposition,the surface properties or surface energies may also be controlled, suchas through the use of resist coatings or by otherwise modifying the“wetability” of such a surface, for example, by modifying thehydrophilic, hydrophobic, or electrical (positive or negative charge)characteristics, or by a corona treatment, for example. In conjunctionwith the characteristics of the compound, suspension, polymer or inkbeing deposited, such as the surface tension, the deposited compoundsmay be made to adhere to desired or selected locations, and effectivelyrepelled from other areas or regions.

For example and without limitation, the plurality of metallic nanofibers100 are suspended in a liquid, semi-liquid or gel carrier using anyevaporative or volatile organic or inorganic compound, such as water, analcohol, an ether, etc., which may also include an adhesive component,such as a resin, and/or a surfactant or other flow aid. In an exemplaryembodiment, for example and without limitation, the plurality ofmetallic nanofibers 100 are suspended as described above in theExamples. A surfactant or flow aid may also be utilized, such asoctanol, methanol, isopropanol, or deionized water, and may also use abinder such as an anisotropic conductive binder containing substantiallyor comparatively small nickel beads (e.g., 1 micron) (which providesconduction after compression and curing and may serve to improve orenhance creation of ohmic contacts, for example), or any other uv, heator air curable binder or polymer, including those discussed in greaterdetail below (and which also may be utilized with dielectric compounds,lenses, and so on).

The optically transmissive, conductive film (150, 150A) formed from thecured or dried metallic nanofiber ink may be utilized in a wide varietyof applications, namely, an application involving a conductor, aconductive ink or polymer or more preferably, an optically transmissiveconductor. Various applications are also illustrated in the relatedapplications, incorporated by reference herein in their entireties.Numerous additional applications will be apparent to those having skillin the art.

Various textures may be provided for the optically transmissive,conductive film embodiment 150, such as having a comparatively smoothsurface, or conversely, a rough or spiky surface, or an engineeredmicro-embossed structure (e.g., available from Sappi, Ltd.) topotentially improve the adhesion of other layers and/or to facilitatesubsequent forming of ohmic contacts with other components such asdiodes 120. The optically transmissive, conductive film embodiment 150may also be given a corona treatment prior to deposition of othercomponents, which may tend to remove any oxides which may have formed,and also facilitate subsequent forming of ohmic contacts. Those havingskill in the electronic or printing arts will recognize innumerablevariations in the ways in which the optically transmissive, conductivefilm embodiment 150 may be formed, with all such variations consideredequivalent and within the scope of the disclosure. In addition, forother various embodiments, the optically transmissive, conductive filmembodiment 150 may be deposited as a single or continuous layer, such asthrough coating or printing, for example.

As may be apparent from the disclosure, an exemplary apparatus 150,150A, may be designed and fabricated to be highly flexible anddeformable, potentially even foldable, stretchable and potentiallywearable, rather than rigid. For example, an exemplary apparatus 150,150A, may comprise flexible, foldable, and wearable clothing, or aflexible lamp, or a wallpaper lamp, without limitation. With suchflexibility, an exemplary apparatus 150, 150A, may be rolled, such as aposter, or folded like a piece of paper, and fully functional whenre-opened. Also for example, with such flexibility, an exemplaryapparatus 150, 150A, may have many shapes and sizes, and be configuredfor any of a wide variety of styles and other aesthetic goals. Such anexemplary apparatus 150, 150A, is also considerably more resilient thanprior art devices.

Although the invention has been described with respect to specificembodiments thereof, these embodiments are merely illustrative and notrestrictive of the invention. In the description herein, numerousspecific details are provided, such as examples of electroniccomponents, electronic and structural connections, materials, andstructural variations, to provide a thorough understanding ofembodiments of the present invention. One skilled in the relevant artwill recognize, however, that an embodiment of the invention can bepracticed without one or more of the specific details, or with otherapparatus, systems, assemblies, components, materials, parts, etc. Inother instances, well-known structures, materials, or operations are notspecifically shown or described in detail to avoid obscuring aspects ofembodiments of the present invention. One having skill in the art willfurther recognize that additional or equivalent method steps may beutilized, or may be combined with other steps, or may be performed indifferent orders, any and all of which are within the scope of theclaimed invention. In addition, the various Figures are not drawn toscale and should not be regarded as limiting.

Reference throughout this specification to “one embodiment”, “anembodiment”, or a specific “embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment and not necessarily in allembodiments, and further, are not necessarily referring to the sameembodiment. Furthermore, the particular features, structures, orcharacteristics of any specific embodiment may be combined in anysuitable manner and in any suitable combination with one or more otherembodiments, including the use of selected features withoutcorresponding use of other features. In addition, many modifications maybe made to adapt a particular application, situation or material to theessential scope and spirit of the present invention. It is to beunderstood that other variations and modifications of the embodiments ofthe present invention described and illustrated herein are possible inlight of the teachings herein and are to be considered part of thespirit and scope of the present invention.

It will also be appreciated that one or more of the elements depicted inthe Figures can also be implemented in a more separate or integratedmanner, or even removed or rendered inoperable in certain cases, as maybe useful in accordance with a particular application. Integrally formedcombinations of components are also within the scope of the invention,particularly for embodiments in which a separation or combination ofdiscrete components is unclear or indiscernible. In addition, use of theterm “coupled” herein, including in its various forms such as “coupling”or “couplable”, means and includes any direct or indirect electrical,structural or magnetic coupling, connection or attachment, or adaptationor capability for such a direct or indirect electrical, structural ormagnetic coupling, connection or attachment, including integrally formedcomponents and components which are coupled via or through anothercomponent.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention. To the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

Furthermore, any signal arrows in the drawings/Figures should beconsidered only exemplary, and not limiting, unless otherwisespecifically noted. Combinations of components of steps will also beconsidered within the scope of the present invention, particularly wherethe ability to separate or combine is unclear or foreseeable. Thedisjunctive term “or”, as used herein and throughout the claims thatfollow, is generally intended to mean “and/or”, having both conjunctiveand disjunctive meanings (and is not confined to an “exclusive or”meaning), unless otherwise indicated. As used in the description hereinand throughout the claims that follow, “a”, “an”, and “the” includeplural references unless the context clearly dictates otherwise. Also asused in the description herein and throughout the claims that follow,the meaning of “in” includes “in” and “on” unless the context clearlydictates otherwise.

The foregoing description of illustrated embodiments of the presentinvention, including what is described in the summary or in theabstract, is not intended to be exhaustive or to limit the invention tothe precise forms disclosed herein. From the foregoing, it will beobserved that numerous variations, modifications and substitutions areintended and may be effected without departing from the spirit and scopeof the novel concept of the invention. It is to be understood that nolimitation with respect to the specific methods and apparatusillustrated herein is intended or should be inferred. It is, of course,intended to cover by the appended claims all such modifications as fallwithin the scope of the claims.

It is claimed:
 1. A method of manufacturing a substantially transparentconductor, the method comprising: depositing a composition on asubstrate, the composition comprising: a plurality of metallicnanofibers, substantially all of the metallic nanofibers at leastpartially coated with a first polymer comprising polyvinyl pyrrolidone(PVP) having a first molecular weight; a first solvent comprisingcyclohexanol; and a second polymer or polymeric precursor mixed with thecyclohexanol and comprising polyvinyl pyrrolidone (PVP) having a secondmolecular weight greater than the first molecular weight; and formingthe substantially transparent conductor by heating the composition for apredetermined period of time.
 2. The method of claim 1, wherein the stepof heating further comprises: ramp curing the composition by heating thecomposition beginning at a first temperature and gradually orincrementally increasing the temperature to a second temperature, thesecond temperature less than or equal to 160° C.
 3. The method of claim2, wherein the predetermined period of time is from four minutes to sixminutes.
 4. The method of claim 1, wherein the second molecular weightis greater than 500,000.
 5. The method of claim 1, wherein the firstmolecular weight is less than 50,000.
 6. The method of claim 1, whereinthe plurality of metallic nanofibers have lengths between 1μ and 250μand diameters between 10 nm and 500 nm.
 7. The method of claim 1,wherein the plurality of metallic nanofibers comprise silver, alloysthereof, and mixtures thereof.
 8. The method of claim 1, wherein thecomposition further comprises: a second solvent selected from the groupconsisting of: water; alcohols; cyclic alcohols; lactones; cyclicketones; glycols; glycerols; carboxylic acids; dicarboxylic acids;tricarboxylic acids; alkyl carboxylic acids; and mixtures thereof. 9.The method of claim 1, wherein the composition further comprises: asecond solvent different from the first solvent, wherein the secondsolvent comprises 1-butanol.
 10. The method of claim 1, wherein thefirst solvent is present in an amount of 0.05 percent to 99.95 percentby weight of the composition.
 11. The method of claim 1, wherein thecomposition further comprises: a polyimide present in an amount of 0.75%to 5% by weight of the composition.
 12. The method of claim 1, whereinthe composition further comprises: a second solvent different from thefirst solvent.
 13. The method of claim 12, wherein the second polymer orpolymeric precursor is present in an amount of 0.75% to 5% by weight ofthe composition.
 14. The method of claim 13, wherein the second solventcomprises 1-butanol and is present in an amount of 3 percent to 10percent by weight of the composition and the first solvent is present inan amount of 50 percent to 95 percent by weight of the composition. 15.The method of claim 14, wherein the composition further comprises: anorganic acid present in an amount of 0.1% to 2% by weight of thecomposition, the organic acid comprising at least one acid selected fromthe group consisting of: carboxylic acids, dicarboxylic acids,tricarboxylic acids, alkyl carboxylic acids, acetic acid, oxalic acid,mellitic acid, formic acid, chloroacetic acid, benzoic acid,trifluoroacetic acid, propanoic acid, butanoic acid; and mixturesthereof.
 16. The method of claim 12, wherein the second solvent is atleast one solvent selected from the group consisting of: water;alcohols; cyclic alcohols; lactones; cyclic ketones; glycols; glycerols;carboxylic acids; dicarboxylic acids; tricarboxylic acids; alkylcarboxylic acids; and mixtures thereof.
 17. The method of claim 16,wherein the composition further comprises: a third solvent, the thirdsolvent different from the first solvent and the second solvent, thethird solvent present in an amount of 0.1% to 10% by weight of thecomposition.
 18. The method of claim 17, wherein the third solvent is atleast one solvent selected from the group consisting of: water;alcohols; cyclic alcohols; lactones; cyclic ketones; glycols; glycerols;carboxylic acids; dicarboxylic acids; tricarboxylic acids; alkylcarboxylic acids; and mixtures thereof.
 19. The method of claim 12,wherein the plurality of metallic nanofibers are present in an amount of0.01% to 10.0% by weight of the composition; the second solvent ispresent in an amount of 1% to 10% by weight of the composition andcomprises at least one solvent selected from the group consisting of:1-butanol, ethanol, 1-pentanol, 1-hexanol, n-methylpyrrolidone, aceticacid, cyclohexanone, cyclopentanol, butyl lactone, and mixtures thereof;wherein the second polymer or polymeric precursor is present in anamount of 0.75% to 5.0% by weight of the composition; and the firstsolvent is present in an amount of 1.75% to 98.25% by weight of thecomposition.
 20. The method of claim 1, wherein the composition has aviscosity substantially between 200 cps and 20,000 cps at 25° C.
 21. Themethod of claim 1, wherein the step of depositing further comprises:printing the composition to form an electrical contact.
 22. The methodof claim 1, wherein the composition further comprises: polyvinyl alcoholmixed with the polyvinyl pyrrolidone and the cyclohexanol.
 23. A methodof manufacturing a substantially transparent conductor, the methodcomprising: depositing a composition on a substrate, the compositioncomprising: a plurality of metallic nanofibers, the plurality ofmetallic nanofibers comprising silver, alloys thereof, and mixturesthereof, substantially all of the metallic nanofibers at least partiallycoated with a first polymer comprising polyvinyl pyrrolidone (PVP)having a first molecular weight; a first solvent comprisingcyclohexanol; and a second polymer or polymeric precursor mixed with thecyclohexanol and comprising polyvinyl pyrrolidone (PVP) having a secondmolecular weight greater than the first molecular weight, and whereinthe second molecular weight is greater than 500,000; and forming thesubstantially transparent conductor by heating the composition for apredetermined period of time beginning at a first temperature andgradually or incrementally increasing the temperature to a secondtemperature, the second temperature less than or equal to 160° C. 24.The method of claim 23, wherein the predetermined period of time is fromfour minutes to six minutes.
 25. The method of claim 23, wherein thefirst molecular weight is less than 50,000.
 26. The method of claim 23,wherein the composition further comprises: a second solvent differentfrom the first solvent and selected from the group consisting of: water;alcohols; cyclic alcohols; lactones; cyclic ketones; glycols; glycerols;carboxylic acids; dicarboxylic acids; tricarboxylic acids; alkylcarboxylic acids; and mixtures thereof.
 27. The method of claim 26,wherein the composition further comprises: a third solvent, the thirdsolvent different from the first solvent and the second solvent, thethird solvent present in an amount of 0.1% to 10% by weight of thecomposition, wherein the third solvent is at least one solvent selectedfrom the group consisting of: water; alcohols; cyclic alcohols;lactones; cyclic ketones; glycols; glycerols; carboxylic acids;dicarboxylic acids; tricarboxylic acids; alkyl carboxylic acids; andmixtures thereof.
 28. The method of claim 23, wherein the first solventis present in an amount of 0.05 percent to 99.95 percent by weight ofthe composition and wherein the second polymer or polymeric precursor ispresent in an amount of 0.75% to 5% by weight of the composition. 29.The method of claim 23, wherein the composition further comprises: anorganic acid present in an amount of 0.1% to 2% by weight of thecomposition, the organic acid comprising at least one acid selected fromthe group consisting of: carboxylic acids, dicarboxylic acids,tricarboxylic acids, alkyl carboxylic acids, acetic acid, oxalic acid,mellitic acid, formic acid, chloroacetic acid, benzoic acid,trifluoroacetic acid, propanoic acid, butanoic acid; and mixturesthereof.
 30. A method of manufacturing a substantially transparentconductor, the method comprising: depositing a composition on asubstrate, the composition comprising: a plurality of metallicnanofibers, substantially all of the metallic nanofibers at leastpartially coated with a first polymer comprising polyvinyl pyrrolidone(PVP) having a first molecular weight; a first solvent comprisingcyclohexanol; a second solvent different from the first solvent, whereinthe second solvent is at least one solvent selected from the groupconsisting of: water; alcohols; cyclic alcohols; lactones; cyclicketones; glycols; glycerols; carboxylic acids; dicarboxylic acids;tricarboxylic acids; alkyl carboxylic acids; and mixtures thereof; and asecond polymer or polymeric precursor mixed with the cyclohexanol andcomprising polyvinyl pyrrolidone (PVP) having a second molecular weightgreater than the first molecular weight, and wherein the secondmolecular weight is greater than 500,000; and forming the substantiallytransparent conductor by heating the composition for four minutes to sixminutes beginning at a first temperature and gradually or incrementallyincreasing the temperature to a second temperature, the secondtemperature less than or equal to 160° C.